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THE UNIVERSITY

OF ILLINOIS

LIBRARY



AGRICULTURAL
LIBRARY



BULLETIN No. 220



BLACK SPOT OF ONION SETS



BY FEANK LINCOLN STEVENS
AND ESTHER YOUNG TRUE




TIRBANA, ILLINOIS, MAY, 19] 9



CONTENTS OF BULLETIN No. 220

PAGE

INTRODUCTION 507

THE DISEASE 507

The Three Types 508

THE CAUSAL FUNGUS 509

Culture Studies 509

The Subicle 510

The Tubercle 510

THE PERITHECIUM 511

CORRELATION WITH EARLIER MORPHOLOGICAL WORK 529

TAXONOMIC POSITION OF THE ASCIGEROUS STAGE 529

SUGGESTIONS REGARDING CONTROL 531

BIBLIOGRAPHY . . 532



BLACK SPOT OF ONION SETS

VOLUTELLA CIRCINANS AND ITS PERITHECIAL FORM,
CLEISTOTHECOPSIS CIRCINANS

BY FRANK LINCOLN STEVENS, PROFESSOR OF PLANT PATHOLOGY, UNIVER-
SITY OF ILLINOIS, AND ESTHER YOUNG TRUE, RESEARCH ASSISTANT,
IN COOPERATION WITH THE DEPARTMENT OF HORTICULTURE

INTRODUCTION

Serious losses of onions during storage, particularly of onion
sets, led to the present study. Loss in storage, especially of the
white varieties, is very high. It is estimated that in the Chicago
district alone, for the 1917 season, there was a loss of approximately
150,000 bushels of sets valued at about $300,000.

In the present study onions and onion sets were examined cither
directly in the markets and stores or by sample lots which were sup-
plied by large holders. Results of such examinations showed the
presence of several fungi apparently as the cause of loss in storage,
as follows: "Vermicularia," Sclerotium, Botrytis (several species),,
Fusarium, Aspergillus, Bacillus, and a few apparently saprophytic
forms. The so-called " Vermicularia" was present in 60 to 80 per-
cent of the white onion sets examined, and Sclerotium in 2 to 7
percent. The other fungi appeared in a lesser quantity. It is to the
fungus found most generally present that chief attention has been
given in the studies reported in this bulletin.

THE DISEASE

This disease is easily recognized by both macroscopic and mi-
croscopic observation. As a disease it was first described under the
name " V ermicularia, circinans" by Berkeley in Gardener's Chronicle
in 1851. ia It has later been referred to by Clinton, 2 Cooke, 3 Hal-
sled, 4 Massee, 5 Selby, Stevens, 7 Stevens and Hall, 8 Stoneman, 9
Thaxter, 10 Tubeuf and Smith, 11 Voglino, 12 and a few others. It has
been reported under many common names, such as anthracnose, rot,
smudge, surface rot of the bulb, mold, vermiculariose, black spot,
and neck rot. The records of the Plant Disease Survey, U. S. De-
partment of Agriculture, show its distribution in the following
states : Connecticut, Indiana, Louisiana, Maryland, Massachusetts,
Minnesota, New York, Ohio, Pennsylvania, Texas, and Wisconsin.

"Superior figures are used thruout this bulletin to indicate the literature cita-
tions given in the bibliography, page 532.

507



508 BULLETIN No. 220 [May,

THE THREE TYPES

The disease assumes three distinctly different aspects, which are
here described separately as Types A, B, and C.

Type A. This type of the disease is the most common and the
most striking in appearance. It is the one that is usually regarded
as typical and the one commonly described and figured as the onion
disease due to " Vermicularia. " Upon the dry outer scale of the
bulb it presents an approximately circular spot, usually about the
size of a dime or a quarter. The hue is prevailingly black, owing to
much black mycelium within the tissues, and numerous black knots
of mycelium are seen, often grouped in a series of concentric circles,
as shown in Fig. 1 (1). (See also Massee, 5 Fig. 130, and Thaxter, 10
Fig. 44.)

Variations from this typical concentric arrangement are met.
In some instances the prevailing direction of the mycelium is at
right angles to the main veins, resulting in transverse black bands
(see cover illustration). In other instances neither the concentric
nor the banded 'arrangement predominates but the spots consist of
irregularly arranged minute specks, as illustrated in Fig. 1(2). In
still other instances the area involved in the spot is entirely black
and the minute component black specks are lost to view, as in Fig. 1
(3, 4). (See also Clinton, 2 Plate 20, .Fig. a). Another view of the
condition shown in Fig. 1 (1) and in the cover illustration is
shown in Fig. 2 (1). In many of these spots there is a pronounced
tendency for the fungus to follow the course of the veins, as may be
seen in Fig. 2 (2). All of the varying forms of Type A occur on
the outermost scales of the bulb, as in Fig. 2 (3), and in all cases
on scales which are perfectly dry.

Type B. This type, like Type A, occurs on the dry outer scales
but it is usually limited to the upper part of the bulb, as illustrated
in Fig. 3(1); at least it always starts at the top of the bulb and
progresses toward the base. This type may assume any of the vari-
ations mentioned under Type A. Several views are shown in Figs. 4
and 5. The essentially distinguishing character of this type is that
the invasion of the fungus starts at the top of the bulb, usually stop-
ping with the drying of the scale before the equatorial region is
reached. It is probable that Type B results from infection thru the
wounds caused in removing the "top."

Type C. This type is manifest in those scales of the bulb which
are still succulent and juicy or which remained so for considerable
time after the invasion by the fungus. As shown in Fig. 3 (2), the
spots may lie directly under and originate from spots of Type A,
but on account of their very different appearance and character
this type is described separately. Fig. 3 (3) shows Type A; Fig. 3



1919] BLACK SPOT OP ONION SETS 509

(4) shows the same bulb as Fig. 3 (3) but with the outer scale re-
moved, showing Type C below. In Type C the fungus, owing to the
fact that it lives and develops for a longer time within the juicy tis-
sue, attains developmental stages not shown in the more limited life
period in the outer scales. The chief manifestation of this develop-
ment is in the formation of tubercles, or warty growths. These are
usually located at the centers of the infected areas, whether the spot
is small, 2 to 3 mm., or larger, .5 to 1 cm. In the| older, larger spots,
secondary or tertiary series of tubercles may occur, often in roughly
concentric arrangement. The tubercles are frequently 1 or even
2 mm. in diameter and rise fully 1 mm. above the surrounding scale.
The distinguishing character of this type is the presence of these
tubercles and the fact that the disease often remains progressive,
tho of course scales with the tubercular development may later dry
and thus inhibit further progress.

That these three types of disease are due to the same fungus is
fully borne out by the study of the culture characters, by the micro-
scopic studies detailed below, and by the fact that the types to an
extent merge one into the other.

THE CAUSAL FUNGUS

The mycelium is rather coarse, 3.6 to 10.8 ^ wide, branches fre-
quently and irregularly, and is cut by septa at irregular intervals,
usually about 12 to 16 ^ apart. It is crooked, intercellular, and
intracellular, or even superficial (Figs. 8, 9, 10). When young it
is hyaline, later turning quite dark. The fungus shows a strong
tendency to develop mats of parallel hyphae, as illustrated in Fig. 7
(3). It is these that are largely responsible for the banded appear-
ance, shown in the figure on the front cover. It is also characteris-
tic of the mycelium to produce branches, the terminal cells of which
turn dark and swell, producing an effect much like that of the so-
called appressoria of the germinating anthracnose spores. Inter-
calary cells also often darken and swell, as do frequently whole
series of cells.

CULTURE STUDIES

Studies of the fungus in agar showed general agreement with
the facts stated above. The methods used in isolating the fungus
were: direct planting on plates of small pieces of infected onion
tissue; dilution plating of spores in agar; and direct planting of
spores which had previously germinated. For most of the studies an
onion-broth agar was used.

When white onions were used in the agar, the growth of fungus
was abundant ; when yellow and red onions were used, the growth
was slight and not many sporing bodies developed. In Petri-dish



510 BULLETIN No. 220 [May,

cultures the fungus produced a light-colored mycelium near the up-
per surface of the medium and under some conditions an aerial
mycelium. Contrasting the structure with that found on the onion
in nature, the cells of the mycelium were much more elongated and
very seldom was there an appearance of oil drops in them. More-
over, on agar there were very few of the dark, swollen end cells so
characteristic of the fungus under natural conditions. As the col-
ony became older, the aerial mycelium gradually shriveled and the
colony assumed a gray or grayish-brown color with numerous small
protuberances on the surface. These are the sporodochia, acervulus-
like structures on subicles of interwoven hyphae. They were not
confined to the upper surface alone but often developed below the
surface of the agar. Many of the sporodochia were seen to have a
pedicel, or neck, arising from the subicle. As the fungus grew older,
it often colored the medium a dark brown. A portion of an agar
plate showing a colony is shown in Fig. 15, The small black dots
seen are the sporodochia.

THE SUBICLE

As the fungus ages, the mycelium in numerous points develops
subicles, which are at first one cell thick. Various stages are shown
in Figs. 6 (1, 2, 3), 7 (3), and 12 (1). The subicle may attain
dimensions of 224 to 784 p by 336 to 1,344 /x. Often setae appear
upon it, varying in number from one to many, as shown in Figs. 6
(1, 3) and 7 (3). Fig. 12 (1) shows one of these setigerous subicles
in section. The setae are 125 to 240 fi long, about 4 p. wide at the
base, acute at the apex, and very dark in color.

THE TUBERCLE

"When the fungus grows for a sufficient time in the still juicy
scale, numerous host cells as well as intercellular spaces become
filled and largely distended with mycelium, as shown in Fig. 8
(1, 2, 3). This results in greatly increasing the thickness of the host
at these points, producing distinctly swollen spots (Figs. 9 and 10).
The subicles, present superficially over these regions, increase in
thickness by division of the cells in a direction tangential to the sur-
face of the onion, resulting in distinct rounded protuberances, or
tubercles. Several stages in the development of these structures arc
shown in Fig. 11 (1, 2, 3, 4).

The Sporodocliium. This is seen to consist of a pseudoparenchy-
matous inner tissue covered by a continuous surface layer. It may
or may not bear setae in the early stages of development. The young
sporodochium eventually ruptures its covering membrane. Occa-
sionally the surface is overgrown by loose mycelial masses, as shown
in Fig. 12 (2).



19 19] BLACK SPOT OF ONION SETS 511

When sufficient growth time allows, especially when one of the
deeper scales of the onion is affected, the sporodochium increases
largely in diameter, reaching even more than 2 mm., and becomes
nearly flat-topped or corrugated, as shown in Figs. 13 (2), 14, and 16.
In all cases the conidiophores are borne upon a raised superficial
base which constitutes the sporodochium (see Figs. 13 (1, 2), 14, and
16), in contradistinction to the innate form of the acervulus, which
has no such base. The tubercular swelling, due to the massing of
mycelium below and in the epidermis, partakes of sporodochial char-
acter also, and while this subepidermal part may not be regarded as
constituting a true sporodochium, it serves to emphasize the tendency
of the fungus to produce such structures.

Conidiophores. Soon after rupturing the covering membrane,
the sporodochium develops on its surface numerous parallel coni-
diophores of palisade arrangement, as shown in Figs. 12 (3) and 13
(1, 2, 3). Interspersed with the conidiophores are few or many
setae. The conidiophores are 24 to 48 /x long, 2.4 p. thick, straight,
simple, hyaline, few-septate, obtuse, and bear the conidia acro-
genously.

Conidia. The conidia are falcate, acute at each end, continuous,
hyaline, 19.2 to 26.4 /x by 3.6 to 7.2 /x. In germination they become
one-septate and send out germ tubes from one or both cells, from
either the side or the tip of the spore. Appressoria similar to those
produced by Gloeosporium are also found in abundance.

THE PERITHECIUM

Onion sets which were heavily infected with the fungus under
discussion were placed in sand in the greenhouse. Upon examination
of certain of these sets after about thirty days, black bodies were
seen on the outer scales. Some of these were imbedded for micro-
tome sectioning; others were examined direct.

These structures, the perithecia, are irregularly globular, dark
brown to black, and from 89.6 to 313.6 p. in extreme dimensions.
The surface is characteristically reticulated, as seen in Fig. 17 (1),
and there are often numerous short hairs growing from the surface
cells. The perithecia are borne either in or on the host tissue. Or-
ganically connected with the perithecia is the typical mycelium of
the Volutella, a point that is especially clear in the study of young
perithecia. Fig. 17 (3). There is no ostiole. Microtome sections
show the perithecia in early stages to resemble sclerotia in general
structure, i. e., the whole structure is pseudoparenchymatous, the cells
of the outer layer being darker and thicker-walled than those of the.
interior. This point is illustrated in Fig. 17 (1 and 4). In a later
stage an ascogeiums region is differentiated. This assumes the



512 BULLETIN No. 220

form of numerous filiform hyphae of nearly parallel direction aris-
ing from the basal portion of the perithecium, as shown in Fig. 18 (2) .
Perithecia of this age when crushed release this ascogonium en masse.
In still older perithecia the central part is filled with asci, lying in
close contact and without paraphyses, as seen in Fig. 18 (3). In
still later stages the asci disappear and the ascospores lie free in the
perithecial cavity. Figs. 18 (4) and 19. In Fig. 17 (4) is shown
a perithecium in a very early stage of development ; general views
of ascigerous perithecia are shown in Figs. 18 (3, 4) and 19. The
asci are here seen to arise approximately from a region which may
be designated as basal, i. e., not in Plectascinaceous fashion. The
asci are about 72 to 96 p, by 19.2 to 24 /x and are evanescent, disappear-
ing early.

The spores are dark, obtuse at each end, 24 to 36 /x by 9.6 to
14.4 p., muriform, usually with 4 to 7 /* transverse and 1 to 2 /x longi-
tudinal septa, as seen in the optical section shown in Fig. 17 (2).
Two variant spores were found (in situ in microtome section), each
with one septum, Fig. 17 (2). These would be regarded as immature
except for the fact that they were of mature color. It is probable
that the spores do really show this extreme variation in septation
and that the septa may increase greatly in number even after ma-
turity of the spores.

The evidence that these perithecia belong to the Volutella may
be summarized as follows: (1) they occurred on sets badly infected
with the Volutella; (2) no other fungi or other types of mycelium
were seen to be connected with them; (3) when studied in various
stages of development, the typical Volutella mycelium, which offers
definite characters for recognition, was seen in organic connection
with them, as illustrated in Fig. 18 (1) ; (4) the outgrowths from
the perithecia are like those of the Volutella.




FIG. 1. VOLUTELLA, TYPE A: (1) SHOWING CONCENTRIC ARRANGEMENT OF
FUNGUS KNOTS; (2) BLACK SPECKS IRREGULARLY ARRANGED THRU THE SPOTS;
(3) DIFFUSE, NEARLY STRUCTURELESS, BLACK BLOTCHES; (4) SAME AS (3)



513







FlG. 2. VOLUTELLA, TYPE A: (1) OTHER VIEWS OF PORTIONS SHOWN

IN FlG. 1 (1) AND IN THE COVER ILLUSTRATION; (2) ILLUSTRATING A TENDENCY

OP THE FUNGUS TO FOLLOW A VEIN; (3) A PORTION OF THE DRY OUTER SCALE
HAS BEEN REMOVED SHOWING THE FLESHY SCALE BELOW To BE CLEAN AND
HEALTHY



514




FIG. 3. VOLUTELLA: (1) TYPE B. THE SPOT is LIMITED TO THE TOP OF
THE BULB; (2) TYPE C. SPOT IN A LIVING SCALE BELOW A SPOT SUCH AS SHOWN
IN FIG. 1 (1); (3) SHOWING CHARACTERISTIC TYPE A, ALSO TYPE C BENEATH;
(4) TYPE C. SAME AS (3) BUT WITH THE OUTER SCALE REMOVED



515




FlG. 4. VOLUTELLA, TYPE B. SHOWING VARIATIONS IN THE TYPE




FIG. 5. VOLUTELLA, CHARACTERISTIC TYPE B
516




FIG. 6. (1) A SUBICLE BEARING SEVERAL SETAE, H.P. ; (2) SUBICLE SIMILAK
BUT WITHOUT SETAE, H.P. ; (3) SUBICLE IN VERY YOUNG STAGE BEARING ONE
SETA, H.P.



517




FIG. 7. (1) PHOTOGRAPH OF TUBERCLES WITH SETAE AS SEEN IN SIDE VIEW;
(2) A VIEW OP SETOSE TUBERCLE FROM ABOVE; (3) SHOWING MATS OF PARALLEL
HYPHAE DEVELOPED IN EARLY STAGES, ALSO SUBICLES OF COMPARATIVELY LARGE
SIZE, SOME WITH SETAE



518






FIG. 8. (1) SUPERFICIAL MYCELIUM ON A DRIED SCALE, H.P. ; (2, 3) INTERNAL
MYCELIUM IN A DRIED SCALE, H.P.



519




FIG. 9. SHOWING A SUPERFICIAL SUBICLE OVER A VEIN, H.P.




FIG. 10. DRIED SCALE, VOLUTELLA, TYPE A. A SECTION SHOWING THAT THE
FUNGUS Is EPIDERMAL AS WELL AS SUBEPIDERMAL AND SUBCUTICULAR. SHOWING
ALSO THE EELATION OF THE FUNGUS TO THE VEIN, H.P.



520







FIG. 11. (1, 2, 3, 4) EARLY STAGES IN THE DEVELOPMENT OF
THE TUBERCLE, H.P.

521






FIG. 12. (1) A SETIGEROUS SUBICLE IN SECTION, H.P. ; (2) VIEW TO SHOW
THE THICKENING OF THE ONION SCALE BY THE FUNGUS, THE DEPOSITION OF MASSES
OF FUNGUS MYCELIUM, AND THE RELATION TO THE SPORODOCHIUM!, L.P. ; (3) A
SMALL SPORODOCHIUM WITH SETAE AND CONIDIOPHORES ON A DRIED ONION
SCALE, H.P.



522






FIG. 13. A TUBERCLE WHICH HAS EUPTURED AT THE TOP PREPARATORY TO
BECOMING CONIDIIFEROUS AND SETIGEROUS, H.P. ; (2, 3) MEDIAN SECTION THRU A
SETIGEROUS, CONIDIIFEROUS SPORODOCHIUM. A DETAIL OF SETAE, CONIDIOPHORES,

AND CONIDIA, H.P.

523



y








FIG. 14. A LARGE SETIGEROUS, CONIDIIFEROUS SPORODOCHIUM IN MEDIAN
SECTION, L.P. "




FIG. 15. PHOTOGRAPH OF A PORTION OF AN AGAR COLONY X10



524






FIG. 16. MEDIAN SECTION THRU AN OLD, LARGE SPORODOCHIUM. A LOW-
POWER DRAWING SHOWING SHAPE AND KELATION TO THE SUBSTRATUM; THE POR-
TIONS A AND B ENLARGED TO SHOW CELLULAR STRUCTURE, H.P.



525






FIG. 17. (1) A PERITHECIUM IN TANGENTIAL SECTION SHOWING SURFACE
CELLS, ALSO CELLS JUST BELOW THE SURFACE, H.P.; (2) ASCOSPORES, H.P.; (3) A
VERY YOUNG PERITHECIUM, H.P. ; (4) A VERY YOUNG STAGE IN THE DEVELOPMENT
OF A PERITHECIUM, MEDIAN SECTION SHOWING ATTACHMENT TO A BASAL STRUC-
TURE, H.P.



526




527




FIG. 19. MATURE PERITHECIUM IN MEDIAN SECTION. SPORES FREE, H.P.



528



1919} BLACK SPOT OF ONION SETS 529

CORRELATION WITH EARLIER MORPHOLOGICAL WORK

Thaxter in 1889 gave the first American account of this fungus,
placing it in the genus "Vermicularia" because he believed it to be
identical with a fungus described as "Vermicidaria circinans" by
Berkeley in Gardener's Chronicle, in 1851, tho Thaxter clearly was
not satisfied that the fungus was really of pycnidial nature. The
structure which Thaxter figures as " perithecium " in Fig. 45 10 is
clearly identical in character with that shown in the accompanying
Fig. 7(1), and from neither Thaxter 's figure, this figure, nor the slides
made in these studies is there any reason for regarding it as a pycni-
dium. There is at no time in its growth a covered conidial cavity, nor
in fact a conidial cavity of any kind. The structure is a tubercle with
a differentiated cortical outer layer. This outer layer ruptures and
the tubercle develops as a sporodochium.

*

These facts exclude the fungus from the Sph'aeropsidales and
from Vermicularia and place it in the Tuberculariaceae under
Volutella.

Bertha Stoneman, 9 in 1898, made the following statement re-
garding this fungus:

' ' There is not, however, a perithecium developed and altho the fungus has
been placed among the Sphaeropsideae, the character of the pustule shows a close
resemblance to those species of Colletotrichum in which an abundant basal stroma
is developed, while the marginal setae and the elevated basidia, as well as the
characters in artificial cultures, intimately associate the fungus with the genus
Volutella. ' '

The authors fully concur in this view so far as the conidial
stage is concerned.

That the fungus under artificial culture may develop acervuli
rather than sporodochia has led Voglino, 12 followed by Walker," to
class it as Colletotrichum. In the minds of the present writers this
course is not justified, since under its natural conditions the fungus
produces a well-marked sporodochium.

TAXONOMIC POSITION OF THE ASCIGEROUS STAGE

The classification of the ascomycete presents certain difficulties.
It has the general appearance of a Pleospora so far as the character
of the ascus and the fully developed mature spores go, but the peri-
thecium is distinctly unlike a Pleospora in that it has no ostiole, it
is usually hairy, and in general structure it is like an ascigerous cav-
ity developed by a sclerotium rather than the usual perithecium.

"Walker, J. C. Abstract of paper presented at the annual meeting of the
American Phytopathological Society, New York City, Dec., 1916, Phytopath.
Vol. 7, No. 1. 1917.



530 BULLETIN No. 220 [May,

The variation in spore septation is also noteworthy and does not
accord well with a Pleospora.

In general, the perithecium and the mycelium agree well with
the Perisporiaceae, and in that family with the genus Cleistotheca, a
genus with only one representative and that recorded as a sapro-
phyte. Comparison of the material obtained in these studies with
the excellent figure of Zukal 13 gives many points in common. The
differences are chiefly in spore septation, which is irregular in the
present species ; in the arrangement of the asci ; and in the conidial
stages, Cleistotheca possessing a Stachybotryos while this species has
a Volutella as the conidial stage. Were it not for the difference in
conidial forms the authors would place their fungus in the genus
Cleistotheca. However, since the conidial forms are so different, there
is proposed for the perithecial fungus a new genus:

Cleistothecopsis gen. nov.

Characters Uke Cleistotheca except that its eonidial stage is a
Volutella. Type Cleistothecopsis circinans.

Perithecia superficial, irregularly globular, dark brown to
black, no ostiole, surface reticulate, often with numerous short hairs
extending out from surface cells, entirely pseudoparenchymatous,
outer layer of darker thick-walled cells, 89.6 to 313.6 /*.

Asci clavate, basal, evanescent, 8-spored, approximately 72 to
96 /x by 19.2 to 24 p.. Paraphyses present but evanescent.

Ascospores muriform, dark, obtuse at each end, usually with 4 to 7
transverse and 1 to 2 longitudinal septa, 24 to 36 ju, by 9.6 to 14.4 /*.

Its conidial form is the following:

Volutella circinans comb. nov.
Vermicularia circinans Berk.

Sporodochia scattered or often in concentric circles usually in
the centers of infected areas, numerous, black, subepidermal, erum-
pent, becoming covered with loose mycelium, 1 to 2 mm. in diameter,
1 mm. in elevation.

Mycelium hyaline, becoming dark, rather coarse, 3.6 to 10.8 ^
wide, branching irregularly, and with characteristic darkening of end
cells where mycelium is superficial.

Setae one to many, scattered thruout, dark brown to black, 125
to 240 /i long, 4 /x wide at base tapering to apex.

Conidiophores straight, simple, hyaline, few-septate, obtuse, 24
to 48 by 2.4 /*, bearing conidia acrogenously.

Conidia falcate, acute at each end, continuous, hyaline, 19.2
to 26.4 fji by 3.6 to 7.2 /*.



1919} BLACK SPOT OP ONION SETS 531

SUGGESTIONS REGARDING CONTROL

This Volutella reaches its maximum conidial development when
it grows for a considerable time on succulent onions, as for ex-
ample on an inner scale, or rarely on an outer scale if conditions
are such that this remains succulent. When drying of the host
tissue occurs soon after infection, normal conidial development
is precluded. Thus it happens that infection of the outer scale,
which in a comparatively short time dries to papery thinness, leads
in most cases merely to the production of mycelium forming dark
blotches, of subicles bearing few to many setae, of sterile tubercles,
and of sporodochia; but rarely is there sufficient time and succu-
lence for the production of conidiiferous sporodochia in any abun-
dance. These conditions obtain in what has been here designated
as Types A and B, and account for the difference between these


1

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