are noted.
iv TEMPERATURE AND LIFE 205
hand, I think no naturalist, knowing anything about
the mutual interaction of living organisms, would
dismiss the case entirely, and say that any influence
of the one on the other is impossible and incredible.
Alterations in the forms of animals, especially
molluscs, are very frequent, and in some cases a sug-
gestion as to the causes may be gained, when the
deformed animals live under circumstances where a
departure from the normal conditions is obvious. It
is well known that many warm springs contain a large
number of living plants and animals. Physa acuta, for
instance, has been found in waters at 30 Cent (Fischer),
and even at 33 and 35 Cent, (at Dax, according to
Dubalen, in Soc. Linneenne de Bordeaux, vol. xxix.
p. 4), while Turbo thermalis lives at 50 Cent, at
Albano, 1 and Neritina thermophila between 50 and
60 Cent, in New Brittany Island, according to Studer,
etc. But it would seem that when individuals which
have not been gradually accustomed to such con-
ditions, through their ancestors, live for the first time
in such unnatural media, many deformations are apt
to appear. M. G. Regelsperger 2 has observed the
following case. The waters of an artesian well, sunk
1 De Blainville's article Mollusques, in the Dictionnaire des Sciences
Naturelles, 1816-30.
2 Deformations remarquables de Physa acuta observees a Rochefort
surMer. Actes de la Societe Linneenne de Bordeattx, vol. xxxix. (vol. ix.
of 4th series), 1885, p. 117.
206 EXPERIMENTAL EVOLUTION LECT.
many years before, were made to run into a garden.
The water was ferruginous, and its temperature was
32 or 33 Cent, in 1881, when the writer first began
to notice the facts. At that time individuals of
Physa acuta were seen in the water, and it was re-
marked that they were generally small, and in many
cases much deformed, as one may perceive by a
glance at the illustrations which accompany M.
Regelsperger's paper. In 1882 the temperature of the
water had fallen off considerably ; instead of being at
32 or 33 it had decreased to 26*5. M. Regelsperger
again examined the animals, and saw that deformed
individuals were very scarce. Since then the flow of the
water has entirely ceased, the pipes having become im-
permeable, and the part where the animals are seen re-
ceives simply rain-water. Now the animals seem larger
than they were when they lived in warm water, and
none are deformed. In this case it seems quite certain
that the deformations were the result of the heated
water the animals lived in/ and experiments can easily
be made to prove the fact, or to disprove it, as the case
may be. Ritzema Bos l has observed other deforma-
tions, or form-alterations, in very different animals
and circumstances. Tylenchi (Tylenchus devastatrix),
which have been accustomed for some generations to
1 Untersuchungen ilber Tylenchus devastatrix. Biol. Centralblatt,
vii., 1887, pp. 232-243.
iv ENVIRONMENT AND DEFORMATION 207
feed on one single sort of plant, acquire form and size
which differ from those of the same species fed on
other plants, and it even seems that here physiological
variation also comes into play, since prolonged life
on one plant makes them less dangerous for other
sorts of plants.
Deformations may be determined by other natural
causes. M. Pire 1 has seen Planorbis complanatus much
deformed in Belgium through the influence of a thick
layer of aquatic plants on the surface of the pond,
preventing easy access to the air, and S. Clessin 2 ex-
plains the numerous deformations of the Lymnaea
tumida in the Bodensee and Starnbergsee as due to
the constant motion of the surface of these two lakes.
Form may vary in plants also, according to motion
for instance, many plants being much smaller and
much deformed in windy localities. Behrens has
noticed the influence of currents on the forms of
aquatic plants, which E. Mer and others have also
done ; and this leads us to consider the variations in
internal structure, and in functions which are cor-
related with those modifications of external characters.
E. Mer is among those who have investigated the
matter in the most precise manner, and the results
1 Annales Soc. Malacologiqne dc Belgiqtie, vol. vi., 1871, and xiv.,
1879.
a Deutsche- Excursions Molhisken Fauna, Nuremberg, 1876, p. 368.
2o8 EXPERIMENTAL EVOLUTION LECT.
obtained are interesting. His investigations were
made upon amphibious plants. 1 In Ranunculus
aquatilis the external differences are well known
between the plants which grow in water, and those
which live on land, in the length and thickness of the
stem, the length of internodes, etc., and if direct ex-
periment and observation had not shown that the
two forms belong to the same species, they would
certainly be considered as different. Important
structural differences are also present. If we consider
the leaves only, we see that in the aquatic leaf the
dichotomies are from eight to ten in number ; the
cells are cylindrical with two or three hairs ; the
epidermic cells are regularly shaped and contain
chlorophyll, and bear but few stomata ; while in the
air-inhabiting leaf, dichotomies are from two to six
in number ; cells are flattened, without hairs ; epidermic
cells are irregular and contain no chlorophyll, while
they bear a large number of stomata. The same
differences obtain in the leaves of Carex ampullacea
as shown here :
Submerged leaves. Leaves not submerged.
Epidermic cells long, wide, Very thick cuticle. Nu-
without stomata. merous stomata.
2-3 rows of cells with 4-5 rows of cells with abun-
chlorophyll. dant chlorophyll.
1 E. Mer, Des Modifications de Forme et de Structure que subissent les
Plantes suivant qu'elks vegttent a F Air ou sous V Eau. Bull. Soc.
Botanique, 1880, p. 50.
iv ENVIRONMENT AND LEAF-FORMS 209
In a more recent paper Costantin has investigated
the same subject, and given special attention to the
influence of environment on the production of
stomata. 1 In Hippuris vulgaris the leaves which live
in water are long, thin, and sinuous, while in the air
they are short and thick ; in the water the epidermis
consists of short regular cells, bearing a number of
stomata, while in the water the cells are long, thin,
narrow, and bear no stomata. The writer has from
the same rhizome of Polygonum amphibium grown
two plants, one in water, the other in air, and while
the latter was provided with numerous stomata, the
former had none at all. This illustrates well the in-
fluence of environment on the production of stomata,
and in Stratiotes aloides stomata are seen to appear
on the leaves as they gradually emerge above the
surface of the water. But the most minute and
valuable investigations in reference to this matter
have been conducted by M. Pierre Lesage, and were
described last year 2 in his inaugural thesis. His re-
searches bear upon the question of the influence of
1 Costantin, Influence du Milieu Aquatique sur les Stomatcs. Bull.
Soc. Botanique, 1885, p. 259.
2 Pierre Lesage, Influence du Bord de la Mer sur la Structure dcs
Feuilles. Rennes, Oberthur, 1890. See also his Contributions a la
Biologic des Plantes du Littoral et des Halophytes ; Influence de laSalure
sur f Anatomie des Vegetaux, ibid. 1891, which contains an abstract of
many experiments performed after the publication of this thesis.
210 EXPERIMENTAL EVOLUTION LECT.
shore and inland life on different individuals of the
same species, the number of species investigated
being eighty-five. The results have been that in
fifty-four species leaves are thicker in the vicinity
of the sea than in inland individuals ; in twenty-seven
species no difference is apparent ; and in four, leaves
are thicker inland than near the sea. If we consider
that of the fifty-four species above mentioned, seven-
teen are shore-inhabiting plants, while thirty-seven
live preferably inland, it is obvious that, generally
speaking, inland plants acquire thicker leaves when
living in the vicinity of salt water. So much for the
external characters. Now if we consider internal
characters, many differences are detected which ex-
plain the presence of the external differences, and
these differences are observable in all parts of the
leaves. Epidermic cells are larger in twenty-three
shore plants, but in thirty-one there is no differ-
ence, while in four the difference turns to the advan-
tage of inland plants. Here, then, the influence
makes itself but little felt. The case is quite altered
when the mesophyll is considered, for while in eleven
species there is no difference, in all others the palisade
cells are either more numerous or attain greater
thickness, or exhibit both characters at once, and
at the same time the interspaces which underlie
the stratum of palisade-cells are much reduced. The
iv LESAGE'S EXPERIMENTS 211
principal cause of dimensional differences is then to
be found here. And lastly chlorophyll is less abun-
dant in shore-inhabiting individuals. These facts of
observation have been confirmed by experimental
facts. M. Lesage has cultivated plants of the same
species under precisely similar conditions save one,
and has found that the results concur with his obser-
vations. The one condition which differs between the
two sets of cultivations is the presence or absence of
common salt in the water used for watering the plants.
Of two individuals of the same species the one which
has grown in soil watered with salted water has thicker
leaves, and in these leaves the palisade cells are seen
to be larger and more numerous. The experiments
show that the influence exerted by sea-shore life
on plants is principally due to the salt which is always
contained in lesser or greater quantities in the soil,
and is brought there by the winds carrying small
drops of sea-water from the crests of the waves ; they
show at the same time that external variations are
accompanied by important structural differences.
Sea-shore life or the presence of some common salt
in the soil where plants grow exerts even more im-
portant variations ; variations not in morphology
and anatomical features, but in the physiological
processes. In experiments concerning radishes M.
P. Lesage has seen that while in radishes watered
P 2
212 EXPERIMENTAL EVOLUTION LECT.
with common pure water starch is never or but rarely
present in the root at the period when it is generally
eaten, plants of the same age watered with solutions
of common salt (from I to 20 per thousand) do con-
tain a great deal of starch under certain conditions.
For instance, if the water contains 20 per mille of
salt, or i or 2 per mille, there is no starch ; at 3 or
5 /oo tnere is little of it ; at 10 % a little more, but at
4 /oo there is a large amount of starch. Thus, the
presence of common salt, in definite proportions, exerts
a considerable influence on the chemical structure and
physiology of the plant. 1 With Lepidium sativum
things are somewhat different : while the plant con-
tains normally a large amount of starch, watering
with a solution containing 10 / 00 or more of common
salt causes the starch to diminish in a large measure
and even to disappear totally, while weak solutions
do not interfere with the proportions of this sub-
stance. 2
1 Cf. Lesage : Sur la Quantite d'Amidon contenue dans les Tuber-
cules du Radis. Comptes Rendus, September 7, 1891.
2 Cf. Influence de la Salure surla quantite de f Amidon contenue dans
les Organcs vegetatifs du Lepidium sativum (Comptes Rendus, April 20,
1891), and two other notes in the Comptes Rendus, January 18, 1892,
and March 31, 1891. I would also refer the reader, on this general
subject i of 'the influence of salt on structure and physiology, to A.
Batalin : Wirkung des Chlornatriums auf die Entwickelung von
Salicornia herbacea (International Meeting of Botanists and Horti-
culturists in St. Petersburg, 1884) ; and to C. Brick : Beitrage zur
Biologic tind vergleichende Anatomie der baltischen Strandpflanztn
iv SCHMANKKWITSCH'S EXPERIMENTS 213
But external differences seem in some cases to have
much greater moment than has hitherto been re-
cognised, and in this respect no facts are of higher
interest than those which were some years ago made
known by the investigations of a Russian naturalist,
M. Schmankewitsch, 1 to whose work I must call
attention, although most have certainly heard more
or less about it. Daphnia (or Moina) rectirostris is a
small Crustacean which lives indifferently in fresh
water, in brine ditches, and in salt lakes when the con-
centration varies from five to eight degrees of Baume's
areometer. But this difference in life-conditions is
.accompanied by noticeable variations in the physiology
and structure of the animal. The mean temperature of
the salt lake being lower than that of the fresh waters,
Daphnia while being a summer form in the latter
becomes an autumn form in the former, and thus
has acquired the custom of living and even multiply-
ing in salt water at temperatures at which the fresh-
water form cannot live. So much for the physiological
variation. M. Schmankewitsch goes on to say, as
(Schriften der Naturforschenden Gesellschaft zu Dantzig, 1888). Both
authors obtain results which are entirely confirmed by M. Lesage's
investigations.
1 Cf. Zeitschrijt f. Wiss. Zoologie, 1877, vol. xxix., p. 429, and also
the Transactions of the Neo- Russian Society of Naturalists for 1875.
The original papers have been abstracted in Packard's Monograph of
North American Phyllopod Crustacea, 1883, Washington (Geological
Survey).
214 EXPERIMENTAL EVOLUTION LECT.
concerns anatomical characters : "In the females of
the Chadschibai Lake the penicilli or fascicles of knob-
bed setae (Tast-Borsteri) are but little developed, being
nearly fifty times shorter than the antennae themselves,
while in the females of fresh water the same sensitive
penicilli are moderately long and only six times
shorter than the entire antennae. In the males the
sensitive rods are also shorter than in those males
inhabiting fresh water. The small hooks situated
near the sensitive rods on the tips of the male
antennae of fresh-water forms are strongly curved
with pointed tips, while in the males of Chadschibai
Lake those hooks are shorter, less curved, and with
blunt tips. Of the two pointed pale sensory threads
situated on geniculated protuberances of the first
posterior third section of the male antennae, the
posterior one is a little shorter than the anterior
thread, the latter coming out a little more in front.
These threads are, in the males of Dqphnia rectirostris
of the Chadschibai Lake, not in a straight but in a
screw-like line. The distance between the threads is
considerable, which character in the fresh-water males
is much less prominent." I should scarcely have
ventured to quote the foregoing lines, and to enter into
such very minute details, if it was not a fact familiar
to all that many zoologists are to be found in all
countries who spend their life in establishing new
iv SCHMANKEWITSCH'S EXPERIMENTS 215
species which are often based on characters such as
those which Schmankewitsch refers to. These are
specific characters, or at least we are told so every
day by any number of systematic zoologists, and they
are supposed to know " all about species," so we may
go on with the quotation. " Besides the differences
observed in the antennae of the salt-water generations
of Moina rectirostris, our attention is called to the
number of slender finely-toothed spines which occur
on the lateral surface of the post-abdomen of Daphnia
rectirostris, running in lateral series and nearly parallel
with the direction of the rectum. Leydig called them
finely-feathered spines, which I would have called
triangular laterally dentate plates. However this
may be, we observe in our fresh-water forms of
D. rectirostris on each side from eleven to thirteen of
these spines or plates, and only from seven to nine
in the salt-lake form, meaning here, as a matter of
course, mature individuals only. In younger specimens
there are fewer spines than in the adults of the same
surroundings, and therefore the young fresh-water
forms have the same number of spines at a certain
age as the adult forms of the salt lake, which demon-
strates the retarded development of the latter." And
further on : " We now find, in comparing the fresh-
water generations with the salt-water generations of
Daphnia rectirostris, that the latter generations are
216 EXPERIMENTAL EVOLUTION LECT.
not only changed in consequence of the immediate
effect of the surrounding elements, but also in con-
sequence of retarded development under their influ-
ence ; and, furthermore, that sexual maturity shows
itself in the salt-water generations earlier than the
complete typical development of the body-parts.
The termination of the sensory antennae, the colour
of the body, the lesser pinnulation of the bristles in
the salt-water generations are principally dependent
upon the immediate effect of the surrounding elements.
The smaller number of the above-mentioned spines
on the post-abdomen principally depends upon the
retarded development under the influence of changed
surroundings."
We thus see that the change of environment makes
itself felt in various changes in the anatomy and
physiology of the species investigated. The same
conclusion holds good in the case of Branchipus
ferox, another Crustacean which inhabits both salt
and fresh waters. The differences relate to the
length which the egg-sac attains, the segments
of the animal, its shape, the length of the furcal
lobes, and the bristles of the latter. " The most
important difference," says Schmankewitsch, " con-
sists in that while in Branchipus ferox of our salt
ditches the furcal lobes have both edges bristled, in
the fresh-water form only the inner edges of the lobes
iv SCHMANKEWITSCH'S EXPERIMENTS 217
are bristled, etc." And he again says, " Had I not
found all possible transitory forms between salt-ditch
and fresh-water specimens, had I not convinced my-
self of the variability by domestication of this form, I
should have regarded the salt-lake specimen as a new
form."
Other investigations have shown M. Schmankewitsch
that Daphnia degenerata is merely a changed and
degraded variety of D. magna, while the latter is an
intermediate form between the typical D. magna and
D. pulex. But among Phyllopods no species seem more
sensitive to the influence of the surrounding element
than the genera Artemia and Branchipus. Changes
in environment are apt to produce such variations in
the same generation that two closely allied forms
hardly admit of distinction. For instance, Artemia
salina, which lives in water whose concentration varies
from 5 to 12 of saltness, exhibits at high con-
centrations (12 or 15) strong tendencies towards the
form of Artemia milhausenii, which is a form able to
live in water at 24 or 25, in water where the
self-deposition of salt is imminent, and between both
forms all transitional types are found, which show that
both are really of the same species, since A. milhau-
senii may be obtained from A. salina through the
increase of the proportion of salt in the water. And we
cannot escape the conclusion that either our species
218 EXPERIMENTAL EVOLUTION LECT.
may be transformed into each other, or that the
characters upon which they are based are worthless
and require a severe revision.
To end with external characters, I shall merely
remind you of the facts which illustrate the influence
of environment on integuments ; merino sheep lose
their wool in warm climates and recover it under cold
skies ; Iceland cattle have short and small horns which
develop well under mild temperature ; the silky cover-
ing of the common hen, in Guinea, becomes trans-
formed in Europe into the feathers we are accustomed
to see on our domestic fowl, etc. Such instances are
very numerous, and since the anatomical change
follows immediately upon the change of conditions,
we are at liberty to ascribe the former to the latter.
But we must now turn to more important changes
in internal structure or functions, which may be
experimentally produced at will through environ-
mental changes.
Schiibeler has shown that seeds may, through a
change in climate and environment, be made to
become larger than usual, and also to exhibit
greater rapidity in the germinating process. At the
same time the plants grown from the seeds are
more coloured than in their accustomed climate. This
fact may be ascribed to the influence of the greater
light in northern regions, and light, it is known, is apt
iv ENVIRONMENT AND PLANT LIFE 219
to make up for temperature, within some limits, in
plant growth, as De Candolle and others have shown.
At all events the fact that climate or environment
reacts on the germinative faculty is a positive one.
It is well known that the same animals or plants,
in different climates or conditions, exhibit marked
differences in their physiology and intimate functions.
Grape-vines transferred from the Rhine valley to
Madeira require but a few years to yield Madeira
wine, very different from the Rhine wines. It seems,
from the experience of vine-growers, that the taste of
the grapes and wine depends largely upon the chemical
composition of the soil, some soils being very un-
favourable and always yielding wine or grapes of
inferior taste. Of course, differences in taste are due
to variations in the chemistry and physiological pro-
cesses of the plant and fruit. The same fact may
be observed with most vegetables ; all possess a
pleasanter flavour when grown in one sort of soil
than in another. In some cases these internal dif-
ferences are accompanied by external differences,
and M. Saint Lager has thus been led to consider
Ulex major, Trifolium Molineri, Cirsium anglicum,
and Rhododendron ferrugineum as forms of U. parvi-
floruS) T. incarnatum, C. bulbosum, and Rh. hirsutum,
due to the influence of soil containing much silicon,
while the latter inhabit soils containing much lime.
220 EXPERIMENTAL EVOLUTION LECT.
Some mutilations react on the process of fructifica-
tion, if it be true that by cutting through the medulla of
a grape-vine stem, grapes are obtained which contain
no seeds. The fact has been often spoken of for
at least 1,900 years, as ancient Romans practised it,
according to trustworthy witnesses, such as Columella,
Camulogen, and Pliny. 1 At all events the experiment
is worth trying, and some interesting facts might be
derived from it.
Colour variations may be experimentally deter-
mined through changes in environment. Moleschott
has observed that in pure oxygen no black pigment is
generated in the skin of frogs, and the coloration of
birds' eggs sometimes varies with the amount of light
to which they are exposed. These facts are enough
to point the way to many interesting experiments.
We can also produce changes in sexuality, since we
know that the want of suitable depositing ground for
trout, is, according to Barfurth, followed by degenera-
tion and permanent sterility, or at least by the
production of weak forms. In many cases also, defi-
cient nutrition of parents determines predominant
maleness in the progeny, and Giard has shown that
castration parasitaire, as he calls it, that is the presence
1 Cf. Revue Horticole, 1884, pp. 6 and 219; Couverchel, Trait* des
Fruits, 1839 ; Columella, De Arboribus, and also Olivier de Serres,
who knew of the process, but denied its efficacy.
TV WEISMANN'S CRITICISMS 221
of parasites, affects in a marked degree some sexual
characters, males being made thus to resemble more
or less females in external secondary character?, while
complete sterility may be induced through action on
the essential sexual parts.
Fertility may thus be affected in many manners, by
want of space (Semper), by nutrition (Maupas), etc.,
and many facts also go to show that external influ-
ences have a good deal to do with the nature of
segmentation and even with the occurrence of par-
thenogenesis.
As concerns physiological characters, we are also
able to induce much modification, by changes in
pressure for instance, or by altered food, etc. Through
gradual increase of heat we may, as Dallinger has done,
accustom certain Monads to live at temperatures which
are deadly to them in other circumstances ; Chauveau
has shown us how we can profoundly alter the physio-
logical characters of micro-organisms, etc.
At least it seems to us that this conclusion fairly
follows from the foregoing facts. But we cannot