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of the complete reaction, an acceleration being followed by a

From these investigations it is clear that the reaction of the
plant to light is very complex ; that the total effect observed
is the balance of the measures of the accelerating and depressing
influences of light ; and that the magnitude of the effect depends
upon the intensity and the duration of light.

These observations refer to ordinary white light ; analysed
white light has effects on growth according to the particular
rays and to the physiological peculiarity of the species.

Thus Schanz * grew Begonia, Cucumis, Lobelia, Petunia,
and other plants in frames arranged in a series of eight ; by
means of glass of different opacities, all but the first, which
was uncovered, were illuminated by light from which certain
rays had been abstracted :

1. Unaltered day light.

2. Rays longer than 320 pp.

3. Rays longer than 380 pp.

4. Rays longer than 420 pp.

5. Rays longer than 560 pp.

6. Yellow light.

7. Green light.

8. Blue- violet light.

The plants mentioned showed a regular increase in length
from I to 5 inclusive and a decrease from 6 to 8 inclusive.
The behaviour of all plants, however, was not the same ; the
beetroot and the potato developed better in the blue-violet
than in the green, and better in the green than in the yellow.

* Schanz : " Ber. deut. hot. Gesells.," 1919, 37, 430.


In general terms, the more the short rays, especially the ultra-
violet, were removed, the greater the growth up to a certain
limit It also was observed that earlier flowering was pro-
moted by culture under 3 and 4 of the series.

With regard to energy other than light, field experiments
with wheat and other crops show the beneficial action of
overhead electric discharge.* In the year 1915 the increase
in grain and in straw was 30 and 50 per cent respectively
greater than the control, and in 1916 the corresponding figures
were 49 and 88 per cent. The effect of the discharge also
showed itself in the year subsequent to its application ; thus
in the clover and grass crop there was a marked increase in
1916, the year following the treatment. The reasons for the
increase following the stimulation have not yet been found.

WATER. Common experience shows that growth is only
possible provided that the living cells are in a turgid condition,
wherefore circumstances which promote this condition will
promote vegetative growth, but not necessarily reproduction.
The circumstances to which allusion is made are humidity,
adequate soil water, absorption of water and transpiration. A
humid atmosphere promotes vegetative growth in that it re-
duces transpiration ; adequate soil water is necessary if trans-
piration be high ; the absorption of water and its conveyance
to the transpiring surfaces is in part a question of osmosis and
this is bound up with permeability. Although biophysical
problems are outside the present province, it may be mentioned
that any factors which interrupt the normal osmotic adjust-
ments of a plant must adversely affect its vegetative growth.
Thus Dufrnoy has pointed out f that growth is a function of
at least six factors and a variation in any one of these will
influence the velocity of growth. He considers that growth
rate depends upon the balance between the sum of imbibition,
the osmotic pressure of colloids and of the salts of the cell sap,
and the sum of the tension of membranes, the osmotic pres-
sure of the salts of the surrounding medium and the mechani-
cal resistance of the medium.

* Blackman and Jorgensen : " Journ. Board Agric.," 1916, 23, 671 ; 1917,


t Dufr<noy : " Rev. gn. Sci.," 1918, 29, 323.


The vegetative and reproductive phases of a plant are an-
tagonistic, for which reason conditions which promote the one
will degrade the other. Thus generally a low degree of
humidity favours flower production ; red light rays accelerate
the formation of reproductive shoots whilst blue rays retard,
but darkness does not inhibit the formation of flowers at low
temperatures, it is only at higher temperatures that intermit-
tent light and darkness can be made to effect the inhibition.*

NUTRITION. The importance of food is so obvious a
factor governing growth that its consideration would appear
to be unnecessary : but the significance of certain raw materials,
more especially inorganic substances, is so marked as to
warrant some mention.

The following table, results obtained at Rothamsted,f
generally illustrates the action of various chemical fertilizers
on field crops :

WHEAT. (Average yield 1852-1912).

Grain in Straw in

Bushels. Cwts.

Complete minerals 32*1 32-9

Ammonium salts + superphosphate . . . 22*9 22-3

Ammonium salts + superphosphate + sodium sul-
phate 29'! 28*0

Ammonium salts + superphosphate + potassium

sulphate 31*0 31-5

Ammonium salts + superphosphate + magnesium

sulphate 28-8 28

GRASS. (Cut for hay every year).

1918. 1919. 1920.

Complete mineral manure .... 45^2 32-9 46*0 cwts.

Minerals without potash .... 25-9 197 27-3

Complete minerals + ammonium salts . 46*7 53-2 49-6

Minerals without potash + ammonium salts 33-5 34-5 32*6

In this connexion the relative abundance of colloids in the
soil would appear to be of importance ; thus Jennings J finds
that colloids added to the culture medium promoted or de-
pressed the growth of wheat seedlings according to the specific
colloid employed and the concentration of the culture medium.
Agar, for instance, in the presence of low concentrations of

* See Klebs : " Flora," 1918, n, 128.

t For these we are indebted to Dr. W. Brenchley.

t Jennings: "Soil Science," 1919, 7, 201.

VOL. II. 9


nutrient salts increases growth, but in high concentrations a
depression obtains. With regard to inorganic colloids, ferric
and aluminium hydroxides depress whilst colloidal silica in-
creases growth, doubtless because silica is much absorbed by
the cereal grasses and possibly in this form. In view of the
adsorption properties of colloids, the depressing action of
some examples may be due to their adsorbing mineral salts
and thus rendering them unavailable for the use of the plant.
Further, in considering the action of inorganic compounds
on growth, certain important aspects are to be remembered :
the plant has a specific physiology, a good crop of nettles
indicates a high nitrogen content in the soil ; the inter-rela-
tionship of the various compounds concerned, carbohydrate
and nitrogen for instance ; and the fact that conditions which
favour vegetative growth are not necessarily those for re-
productive activity. An abundance of inorganic salts in the
soil favours vegetative activity whilst a relatively small salt
supply is inductive to reproduction ; but this only obtains
provided that other conditions are satisfactory. Thus increase
in growth is impossible for the green plant if carbon assimila-
tion be of a low order of intensity, since carbohydrate is re-
quired for many purposes, structural, respirative, and as raw
material for the elaboration of other compounds such as
proteins. And for this last purpose nitrogen also is necessary ;
wherefore intense carbon assimilation in the absence of nitrogen-
containing substances cannot lead to a growth commensurable
with the intensity of carbohydrate formation. In fact, there is
between nitrogen and carbohydrate a correlation, and growth
is affected according to their ratio. Thus if carbon assimila-
tion be increased by growing plants in an atmosphere enriched
by the addition of carbon dioxide whilst the nitrogen-contain-
ing salts of the soil are not increased, the ratio C/N is high
and the reproductive phase is induced; if, on the other hand,
the ratio C/N is low, the vegetative activity is intensified.*
These results may, however, not obtain if the ratio mentioned
runs to extremes. Kraus and Kraybill f in their experimental
work on the tomato found that a very high C/N ratio results
in but little vegetative growth and but poor reproduction ; a

* Fischer: " Gartenflora," 1916, 65, 232.

t Kraus and Kraybill: "Oregon Agric. Exp. Sta.," 1918, Bull. 149.


medium ratio gives moderate vegetative growth and good re-
production ; and when the C/N ratio is very low, a vigorous
vegetative growth and poor reproduction obtains. Thus the
best results occur when these two factors are reasonably
balanced. From the present aspect the value of these ob-
servations lies in the fact that they provide another instance
in the interaction of the various factors involved in growth :
there is no virtue in increasing the one without duly consider-
ing the others ; heavy manuring with nitrates, for instance,
is mere waste if there be not adequate supplies of water, and
adequate and proportionate supplies of both will not promote
fruit formation in a greenhouse so dimly illuminated as to
depress carbon assimilation.

AUXIMONES. Bottomley * concluded from a large number
of experiments that something more was requisite for the
vigorous growth of a plant than is contained in the ordinary
culture solution made up with mineral substances. These
promoters of growth, the nature and composition of which are
unknown, he termed auximones. Bottomley selected such
plants as Lemna, Salvinia^ and Azolla which normally lead an
aquatic existence and thus avoided the rather artificial condi-
tion inseparable from the cultivation of a terrestrial plant in an
aqueous medium. For healthy growth small amounts of or-
ganic matter are necessary : amongst the best results obtained
were those in which an aqueous extract of bacterized peat had
been added, but other organic substances, such as autoclaved
Azotobacter and crude nucleic acid derivatives from raw peat,
will also serve.

Bacterized peat is sterilized raw sphagnum peat decom-
posed by nitrogen fixing bacteria of the soil ; such treated peat
is considered to act either as a food substance or indirectly
as an accessory food substance. The amount necessary for a
positive result is so small that a body comparable to a vitamin
is suggested. Thus Rosenheim f found that plants of Primula
malacoides treated with an aqueous extract of '1 8 gram of

* Bottomley : " Proc. Roy. Soc.," Lond., B., 1917, 89, 481 ; "Ann. Bot M "
I 92o, 34, 345, 353. See also article in " The Exploitation of Plants," Ed. by F.
W. Oliver, London, 1917. Mockeridge : " Proc. Roy. Soc ," Lond., B., 1917, 89,

f Rosenheim : " Biochem. Journ.," 1917, II, 7.



bacterized peat grew taller than untreated plants. This
aqueous extract contained 20 mgs. of organic matter of which
only I *9 mg. represented nitrogen.

Possibly auximones are connected with the synthesis of
complex nitrogenous molecules, for their action on the nitrogen
cycle organisms is to increase the rate of nitrogen fixation and
nitrification and to depress the rate of denitrification. There
is no doubt that the use of bacterized peat may give marked
positive results in pot cultures, but to what extent the treat-
ment is advantageous to field crops is doubtful.*

HORMONES. The study of regeneration, correlation,
polarity, and cognate subjects f leads to conclusions in some
respects indefinite in that no tangible factor is discoverable that
will account for the beginning or for the control of certain phe-
nomena. A cambium cell divides ; the daughter cell destined
to become a permanent tissue element will develop into a
phloem element if cut off on one side and into an xylem ele-
ment if cut off on the opposite side ; what is it that determines
the fate of the cell ? The leader of a spruce is negatively
geotropic, the lateral branches are diageotropic ; if the leader
be removed, a lateral branch from the topmost whorl will
change its habit, become negatively geotropic and carry on
the functions of the leader. Why must the leader be removed
before a change in tone of a plagiotropic shoot can be effected ?
The primordium of a lateral bud is laid down and, apparently,
all conditions are favourable for development, yet the bud
remains dormant until, say, the apex of the main shoot is re-
moved, then the bud will immediately start its development
It is true that in many cases the diversion of food will account
for the subsequent phenomena but in other instances such an
explanation is inadequate and in such examples the question
is : What is it that presses the trigger ?

The subject properly is beyond the scope of an introduction
to the physiology of metabolism of plants but the introduction

*See Russell: " Journ. Board Agric.," 1917, 24, n.

tSee Bohn : " Compt. rend. Soc. biol.," 1918, 8l, 220. Farmer: "New
Phytol.," 1903, 2, 193, 217. Goebel: "Biol. Zentrbl.," 1916, 36, 193. Lang:
"Brit. Ass. Rep.," 1915, 701. Loeb : " Bot. Gaz.," 1918, 65, 150; "Journ.
Gen. Physiol.," 1919, I, 337.


is desirable even though the acquaintance be not cultivated
until some future occasion.

For long it has been known that very small quantities of
various materials act as powerful stimulants ; the extraordinary
effect of minute traces of zinc on the growth of moulds may be
instanced. Animal physiologists recognize the effect of traces
of substances in stimulating various activities, especially those
associated with secretion. These substances are produced in
one organ and stimulate another organ to which they are con-
veyed by the blood. Hence the idea of a chemical messenger,
or, to use the current term, hormone.

Errera * was amongst the first of botanists to suggest that
hormones play a part in the economy of the plant ; his ex-
planation of the changes in the spruce instanced above is that
the apical shoot continually is secreting an inhibiting sub-
stance which is distributed to other parts of the plant, keeping
them in their normal tone. The removal of the leader of the
spruce removes the source of the inhibiting hormone, where-
fore a near lateral shoot assumes the qualities and functions of
the lost leader.

This idea has been adopted by Loeb f who concludes from
many observations on the development of buds and roots on
the leaves of Bryophyllum calycinum that the apical bud
secretes a hormone which inhibits the development of buds
more basal in position. It is not until the apex is removed
that the buds below will develop.

The degree of inhibition depends on the amount of hormone
and the mass of the lateral bud ; it is presumably for this
reason that the inhibition may only extend to these primordia
situated more immediately below the apex.

This account, brief though it be, will give some idea of the
action of hormones ; the hypothesis, in so far as it affects plants,
however, is not universally accepted. Thus Fyson and Ven-
kataraman \ can find no evidence in favour of the existence of
such bodies, and Child and Bellamy consider that inhibition

* Errera- "British Ass. Rep.," 1904, 814. See also Armstrong: "Ann.
Bot.," 1911, 25, 507.

fLoeb : " Bot. Gaz.," 1915, 60, 249 ; 1916, 62, 293 ; "Science," 1917, 46,
547. See also Reed and Halma : " Plant World," 1919, 22, 239.

% Fyson and Venkataraman : " Journ. Indian Bot.," 1920, I, 337.

Child and Bellamy : " Science," 1919, 50, 362.


is a question of the conduction of stimuli rather than the
movement of tangible substances. Indeed, the evidence re-
garding the occurrence of hormones in plants is nothing like
so conclusive as the proof of their existence in the animal ; ac-
tually, hormones have never been demonstrated in the plant ;
their presence is inferred in order to explain certain very com-
plicated physiological processes otherwise inexplicable.

VITAMINS. During recent years increasing attention has
been given to a class of substances known as vitamins, or
accessory food factors, which play a highly important part in
the dietary of man and animals since their deficiency or ab-
sence may give rise to a variety of so-called deficiency diseases
such as rickets, beri-beri, and scurvy.

Three vitamins are at present recognized and are known
as fat soluble or vitamin A, water soluble or vitamin B, and a
third which may or may not be identical with one of the other
two. As none of these substances have as yet been isolated
in a state of purity, no definite knowledge exists regarding
their chemical composition, and for this reason they are fre-
quently designated by the function which they appear to per-
form in the economy of life. Thus vitamin A is described as
the growth-promoting or anti-rachitic vitamin, whilst vitamin
B is known as the anti-neuritic or anti-beri-beri vitamin, and
the third, for convenience, is known as the anti-scorbutic

The present occasion is not appropriate for a consideration
of the significance and properties such as thermostability re-
sistance to oxidation,* and the chief reason for drawing atten-
tion to vitamins here is the fact that they appear to be
produced only in the vegetable world ; in every case the vita-
min content of animal tissue is dependent on the animal's
nutrition with plant material containing the requisite substance ;
no animal is able independently to produce vitamins for its own

Fat soluble A or the growth-promoting vitamin is, as its
name implies, closely associated with fats or oils and is found
in the animal kingdom in the largest quantities in the oils of
the livers of fish which, in all probability, derive them from

*See " Medical Research Committee" No. 38, H.M. Stationery Office, 1919.


the algae and other plants which form an important part of
the diet of fish.* Amongst animal fats which are poor in vita-
min may be mentioned lard, whilst suet contains a fair propor-
tion. In view of the fact that the plant is the sole source of
vitamin, it is surprising to find that most vegetable oils ob-
tained from plant seeds have a low content of vitamin A, in
fact the storage organs of plants, and especially seeds, contain
little of this substance, f On the other hand, it has been shown
by Drummond and Coward J that large amounts of this sub-
stance are formed in green leaves, where it appears to be as-
sociated with the unsaponifiable portion of the fats rather than
with the protein, and that leaves deficient in chlorophyll ap-
parently are unable to effect its synthesis. Amongst the
marine algae, the green synthesize most, the red being much
less active. Fungi produce no vitamin A.

The suggestion has been made that a probable relation
exists between vitamin A and carotinoids such as carotin and
xanthophyll, a view which has been disputed and, in fact, a
quantitive association between vitamin A and the yellow pig-
ments in the plant tissue is denied.ll Further, there appears
to be no definite relationship between vitamin A and lipo-
chromes in oils and fats.H

With regard to vitamin B, the anti-neuritic or anti-beri-
beri vitamin, it has been shown that this substance is associ-
ated with the pericarp of rice and other grains and the germ
of wheat and rye. The proof of this is furnished by the fact
that the disease of beri-beri is associated with a diet consisting
almost exclusively of polished rice or white wheaten flour in
the preparation of which the pericarp and germ are respectively
removed, whereas rye flour and whole meal, in which the germ
is not entirely removed by milling, retain the active principle.
Whole potatoes, barley and beans also contain the anti-beri-
beri vitamin and the inclusion of these substances or of milk
in the diet ensures immunity from this disease.

* Hjort : " Proc. Roy. Soc.," Lond., B., 1922, 93, 440.

f Drummond and Zilva, "Journ. Soc. Chem. Ind.," 1922, 41, I25T.

+ Drummond and Coward: " Biochem. Journ.," 1921, 15, 530.

Steenbock : "," 1919, 50, 352 ; "Journ. Biol. Chem.," 1921, 46, 32 ;

47. 303 ; 1922, 51, 63.

|| Palmer: "Science," 1919, 50, i; Palmer and Kennedy: "Journ. Biol.
Chem.," 1921, 46, 559.

U" Drummond and Coward: " Biochem. Journ." 1920, 14, 668.


Vitamin C or anti-scorbutic vitamin, on the other hand, is
associated more especially with growing plants for, whereas
dried peas and lentils have no effect in preventing or in curing
scurvy, the same materials, if allowed to germinate, are very
effective anti-scorbutics, which shows that the active material
or vitamin is only secreted by the growing plant and is not
contained in the seed as such.

It has been stated above that there is no definite knowledge
concerning the chemical constitution of the vitamins : various
suggestions have, however, from time to time been put forward
only to be refuted by subsequent work. At the moment, two
views are in the field : the one held by Williams * is that they
are related to hydroxypyridine and contain a betaine ring, the
other, that of Besszonofff is that they are polyphenolic sub-
stances related to hydroquinone.^

* Williams : Journ. Biol. Chem.," 1917, 29, 495.
f Besszonoff : " Compt. rend.," 1921, 173, 466.

JFor further literature on the vitamins see Sherman and Smith: "The
Vitamins," Amer. Chem. Soc. Monograph Series, New York, 1922.



Acer saccharinnm, 100.

Acetone, 81.

Acetic aldehyde, oxidation of, 65.

Acidity, effect on respiration, 92.

of media, 7, 51.

Aerobic respiration, 71.

Alcohol, 100, 101, 119.

Alcoholic fermentation, 100.

Alkaloids, synthesis of, 55.

Almond, n.

Amaranthus, 100.

Amides, 57 59.

Amines, 50.

Amino acids, 50, 51, 54, 56, 58, 59.

Ammonium salts, as source of nitrogen,

50, 5i :

Anaerobic respiration, 71, 100, roi, 103.
Anaesthetics, action of, on respiration, 79.
Andropogon halepensis, 99.
Anthocyanin, 76, 92.
Aponogeton, 27.
Arachis seedling, 12.
Arbutin, effect on respiration, 103.
Asparagine, 58, 59.
Aspergillus, 81, 92.
Assimilation number, 32, 48.
Assimilatory ratio, 41, 45.
Autocatalytic reaction, in, 113, 115.
Autumnal changes, 34.
Auximones, 131.
A vena sativa, 125, see also Oat.
Azolla, 131.
Azotobacler, 131.

Bacillus botulinns, 69.

cholera, 50.

coli, 50.

subtilis, 81, 91.

tetani, 69.
Bacterium aceti, 67.
Bacterised peat, 131.
Barley, 74, 76.

Bean, 74, 86, 88, 89, 101.
Beetroot, 98.
Begonia, 127.
Bomarca, 27.
Brassica alba, 74.
Bryophyllum calycinum, 133.

Buck wheat, 108.
Buffer action, 8.

CACTACEAE, 87, 94, 106.

Carieine, effect on respiration, 81.

Calorie, 62.

Carbon dioxide, effect of, on assimilation,


narcotic effect of, 22, 91 ; rate of ab-
sorption of, 22.
Carbon monoxide, 39, 40, 43, 73.

oxidation of 63.

Carboxylase, 85, 94, 98, 101, 105.

Carpinus betulns, 77.

Catalase, 69, 98, 99, loo.

Catalpa bignonoides, 18.

Ctrutophyllum, 22.

Cherry laurel leaf, 82 ; see also Primus


Chloral hydrate, oxidation of, 65.
Chlorogenic acid, 104, 105.
Chlorophyll, 16, 13, 44, 46, 49.
Chloroform, effect on respiration, 79.
Chromogen, 104.
Cicer arietinum, 59.
Clover, 128.
Coco-nut leaves, 22.
Colloids, effect on growth, 129.
Conditioning factors, 15, 28, 33, 81, 118,

121 ; see also limiting factors.
Crassulaceae, 73.
Cucumis sativus, no, 127.
Cucurbita pepo, 112.
Cyanogenetic glucosides, 60.
Cysteine, 68, 69.
Cystine, 69.

DEHYDRASE, 66, 67, 68.

Dehydrogenation, 64, 65.

Desiccation, effect of, 90.

Dextrose, 36, 37, 92 ; see also Glucose.

Diastase, 83.

Dihydroxy-acetone, 105.

Dipeptide, 68.

Dwarf habit of alpine plants, 58.

Echinocactus, 90.

Electric discharge, effect of, 128.

Elm, 33.

Elodea, 22, 25, 27, 41, 65, 74.




Enzyme limiting assimilation, 34, 48.

Enzymes, 2.

Ether, effect on respiration, 80, 81.

Eucalyptus regnans, 120.

Eurotium, 57.

External factors in assimilation, 16, 17.

FATS as respiratory material, 89 ; syn-
thesis of, 10 ; hydrolysis of, 12.
Fontinalis, 22, 25, 27.
Formaldehyde, 28-31, 39-46.

effect on respiration of Aspergilltis,


peroxide compound of chlorophyll,


Formhydroxamic acid, 53, 54.
Formic acid, 29, 40.
Fructose, 43 ; see also Levulose.


Galanthus nivalis, 36 ; see also Snow-

Gentiana brevidens, 38.

Geotropic stimulation, effect of, on
respiration, 79.

Germination, 12, 58, 74, 75, 84, 87, 88,

100, 101, 102.

Glucose, 101, 105, 119 ; oxidation of, 66.

Glucosides, 56, 60.

Glucuronic acid, 105, 106.

Glutamic acid, 68.

Glutathione, 68.

Glyceric acid, 105.

Glycine, 54.

Glyoxaline, 55.

Glyoxylic acid, 41.

Grand period of growth, no.

Grass, 128, 129.

Growth, 2, 3, 107-136.

rate curve, 109.
Guaiacum, 95.

HEAT of combustion, 61, 62, 70.

fermentation, 70.

respiration, 77.

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