GROWTH OR EVOLUTION OF STRUCTURE IN 
SEEDLING PLANTS* 
THE continuous absorption of oxygen, and formation of car- 
bonic acid, is an essential condition of evolution of structure, 
both in plants and in animals. 
__ The above proposition in so far as it relates to animals will 
probably be admitted by all ; the opposite opinion is, however, 
commonly held as regards plants ; yet we propose to show that 
in these organisms, as in animals, growth as applied to evolu. 
tion of structure, or organisation of material provided, is inse- 
parably connected with oxidation. 
The discussion of the proposition in question necessarily in- 
volves a preliminary view of the character of the gases exhaled 
from yarious plants. Commencing with the lower organisms as 
fungi, the uniform testimony is that these plants at all times 
expire carbonic acid, while it is chiefly in the higher plants, and 
especially in those which contain chlorophyll or green colouring 
matter, that carbonic acid is absorbed and oxygen exhaled. 
The inquiry then in reality narrows itself down to the examination 
of the growth of chlorophyll-forming plants. 
_ Regarding these plants the statement is made and received, 
that they change their action according as they are examined 
the light or in the dark, exhaling oxygen under the first condi- 
jon, and carbonic acid under the second. Various explanations 
of this change of action have been given, that generally accepted 
accounting for it on the hypothesis of the absorption of carbonic 
acid by the roots, and its exhalation by the leaves when light is 
no longer present. 
__ The change, on the contrary, appears to arise out of the fact 
that two essentially different operations have been confounded, 
viz: the actual growth or evolution of structures in the plant, 
and the decomposition of carbonic acid by the leaves under the 
uence of the light, to provide the gum or other materials 
that are to be organised. These two factors are separated by 
Prof. J. W. Draper in his discussion of the conditions of growth 
in plants. We propose to show that by adopting this proposi- 
tion of two distinct operations in the higher plants, all the 
apparent discrepancies regarding the growth of these plants are 
explained. 
he growth of seedlings in the dark offering’ conditions in 
which the act of growth or evolution of structure is accom- 
ished without the collateral decomposition of carbonic acid, 
arranged two series of experiments in which growth under 
this condition might, be studied and compared with a similar 
growth in the light. That the experiments might continue over 
a sufficient period of time to furnish reliable comparative results, 
Iselected peas as the subject of trial, since these seeds contain 
sufficient material to support the growth of seedlings for a 
couple of weeks. 
To secure as far as possible uniformity of conditions between 
the dark and light series, and also to facilitate the separation, 
cleansing and weighing of the roots, each pea was planted in a 
glass cylinder, one inch in diameter and six inches long. These 
cylinders were loosely closed below by a cork, and filled to 
within half an inch of the top with fine earth or vegetable 
‘mould. They were then placed erect in a covered tin box or 
tube stand in such a manner that the lower end dipped into 
water contained in the box, while the whole of the cylinder 
except the top was kept in the dark. Thus the first condition 
for germination, viz., darkness, was secured ; the second, warmth, 
was supplied by the external temperature, which varied from 
70° to 80° F., while regularity and uniformity in the supply of 
moisture in both series was secured by having a box of cylinders 
or tubes for each and keeping the level of the water the same in 
both. The supply of oxygen was also equal and uniform, 
Since the upper part of each tube presented a similar opening 
to the air. : 
Thus prepared, one box containing five cylinders was kept in 
a dark closet, while a second, similar in all respects, was placed 
in a window of an adjoining room, where it was exposed to 
direct sunlight five or six hours every day. Toeach tubealight 
wooden rod thirty inches in length was attached, and on this the 
growth of the seedling was marked every twelve hours. The 
hours selected were 7 A.M. and 7 P.M. I thus obtained the 
night and day, or dark and light growth of every seedling, as 
long as those in the dark grew. The seeds were planted on 
June Ist, and appeared above the ground on June 6th, when the 
measurements were commenced, In each series one seed failed 
* From Silliman’s American Journal of Science and Art, 
NATURE 
373 
to germinate ; the record, consequently, is for four plants in 
each, and the history of the evolution of structures is as follows : 
Evolution of Structure in the Dark.—In Table I. the seeds 
are designated as A, B, C, D, and each column shows the date 
on which leaves and lateral growths appeared. These consti- 
tute periods in the development of the plants, which are indi- 
cated by the number 1, 2, 3, 4, 5, 6. The weight of each seed 
is given in milligrammes, 
Table I.—.Svedlings erown in the Dark 
A. B. c D. 
Weight of seed. 431. 466. 456. 500, 
Period 1, 7th day. 7th day. 7th day. 7th day. 
” 2, 8th ” oth ” gth ” 8th ” 
i Bi a ATOR. <5 Ioth ,, 1ith ,, Ioth ,, 
5 4540 T2th 55 12th ,, E3th .,, T2thaa 
” 5, 14th ” 15th ” 15th ” 14th ” 
a 6; gear 7th, 18th ,, 18th ,, 17th ,, 
A glance at the above shows the uniformity as regards time 
with which the structures were evolyed in each plant. It also 
indicates for each plant an equality in the number of periods of 
evolution, viz., 6, notwithstanding the difference in the weights 
of the seeds, and suggests that the power of evolution of struc- 
ture in seedlings resides in the germ alone. 
The character of the evolution in the six periods shows a 
steady improvement or progression. 
In the first, the growth consists in the formation close to the 
stem of two partially developed pale yellow leaves. 
The second period is similar to the first, except that the leaves 
are a little larger. 
The third presents a pair of small yellow leaves close to the 
main stem, from between which a lateral stem or twig about one 
inch long projects, and bears at its extremity a second pair of 
imperfectly developed yellow leaves, from between which a 
small tendril about a sixteenth of an inch long is given off, 
The fourth resembles the third, the lateral twig being longer, 
and the tendril three times as long as in the third. 
The fifth is like the fourth, except that the tendril bifurcates, 
The sixth is similar to the fifth, except that the tendril trifur- 
cates. 
Stem, leaves, twigs, tendrils of various degrees of complexity, 
all are evolved by the force pre-existing in the germ without the 
assistance of light. 
Evolution of Structure in the Light, 
Table Il,—Seedlings grown in the Light 
E. F. G. H. 
Weight of seed. 288. 426. 462. 544+ 
Period 4 — 6thday, — 6th day 
” 2, 7thday. 7th ,, 7thday. 7th ,, 
” 35 8th ” 8th ” 8th ” oth ” 
As 4, 12th ,, gth ,, Ioth ,, Ioth ,, 
” 5» 15th ” 11th ” 14th ” 12th ” 
” 6, aa ” 13h ,, a ” 14th ,, 
Table II. was obtained in the same manner as Table I, the 
columns representing the days on which lateral growths and 
leaves appeared. Though there is not the same uniformity as in 
Table 1, the periods are identical in both as regards the visible 
character of the evolution Nothing appears in the second that 
did not pre-exist in the first, and in the case of the seeds E and 
G the evolution is even deficient as regards the first and the sixth 
periods, 
While the general character of the evolution in both series is 
similar, certain minor differences exist. In IT. the leaves and 
tendrils are many times larger than in I., and they, with the 
whole plant, are of a bright green colour, instead of the sickly 
pale yellow of I. ; but the light has not developed any new struc- 
ture ; it has only perfected those which pre-existed, and converted 
ae substances into chlorophyll which is not an organised 
jody. 
Not only did the plants in the two series present similarities 
in evolution of structure, but the average weight of dry plant in 
each was very nearly the same, for : 
455 of seeds in the dark produced 184 of dry plant, while 
455 ” light sy = 215 99 
A comparison of the parts below the ground with those 
above (both being dried at 212° F.) shows that the proportion 
bs Toot to total weight of plant was also nearly identical, 
ing, 
