374 
25 of root for 100 of plant in the dark, and 
23 100 light. 
The close similarity in the evolution of visible structure in 
the light and in the dark, the small difference in the total 
weights of the plants grown in the same time in both series, and 
the close approximation in the proportional weight of root to 
plant, all justify the conclusion, that the growth in darkness and 
in light closely resemble each other, and that it is proper to 
reason as regards the nature of the action from the first to the 
second, 
Another interesting fact which lends support to the opinion 
that the process of growth in seedlings developed in the dark is 
very similar to that occurring in those grown in the light, is the 
character of the excrement thrown out by the roots. It is well 
known that many plants so poison the soil that the same plants 
cannot be made to grow therein until the poisonous excretions 
from the roots of the first crop have been destroyed by oxida- 
tion. In the case of peas this poisoning of the soil takes place 
in a very marked manner, and I have found that in the pots in 
which peas have been grown in the dark, the soil is so poisoned 
by the excrements from the roots that a second crop fails to 
sprout. Does it not follow, that since in the two series with 
which I experimented, the excrements from the roots possessed 
the same poisoning action, the processes in the plants from which 
these excrements aaose must have been similar ? 
There remains an important argument concerning which 
nothing has thus far been said. It is to be derived from the 
consideration of the rate of growth in the light series during 
various periods of the day of twenty-four hours. If the eyolu- 
tion of structure in a plant in daylight is the result of the 
action of light, that evolution should occur entirely, or almost 
entirely during the day. If, on the contrary, it is independent 
of the light, it should go on at a uniform rate as in plants in the 
dark. 
For the elucidation of this portion of the subject, I present 
the following tables ; the first of which shows the growth by 
night, 7 P.M. to 7 A.M., of the seedlings in the dark series, com- 
pared with their growth by day, 7 A.M. to 7 P.M. The measure- 
ments were taken from the sixth to the twentieth of the month, 
the day on which growth ceased in the dark series :— 
Table III.—Seedlings grown in the dark 
” ” 
Night growth. Day growth. 
No. 1 12% inches, 14 inches. 
” 2 13¢ ” 13 ” 
Peak: Ii» IIx 55 
» 4 125 5 11g 5, 
Average, 158 ,, Average, 123 ,, 
The total day growth and night growth under these circum- 
stances are nearly equal, though there is a slight excess in favour 
of the night, amounting, as the table shows, to { of an inch in 
12 inches. 
In Table IV. the growth of the light series is given in the 
same manner, by day and by night, for the same time, viz., to 
June 20. The thermometric and hygrometric conditions in 
both series were very similar, as indicated by the dry and wet 
bulb thermometers suspended in the vicinity of each set of 
tubes :— 
Table IV.—Seedlings grown in the light 
Night growth. Day growth. 
No. 5 34 inches 4 inches. 
oe 8 ” 7 ” 
a ¥ 5t ” 43 
” 8 On ” 8} ” 
Average, 6} ,, Average, 6 “ 
In the average, and throughout the table, with a single excep- 
* tion, not only is the uniformity in the rate of growth during the 
day and night shown, but the slight excess of night growth found 
in the series kept in the dark is likewise copied. We must 
therefore accept the conclusion that the act of growth or evolu- 
tion of structure is independent of light, and that the manner of 
growth during the day is similar to that at night. 
It will be noticed that the total average height attained in the 
light is only about half that in the dark series. The explanation 
of this we have already seen in the fact that in the former the 
leaves and tendrils were much larger than in the latter, while the 
dry weights were nearly the same. The material of the seed in 
NATURE 
the light series was consumed in extending these surfaces, wh 
in the dark series it was spent in lengthening the stem. a 
Having established the continuous character of growth in-seed- 
lings, and the similarity of rate and nature of the process by 
night and by day, and admitting that at night plants throw off 
carbonic acid, it is not improbable that this carbonic acid arises, 
not from mechanical absorption by the roots, and vaporisation 
by the leaves, but as a direct result or concomitant of the act or 
process of evolution of structure. 
To put the matter in the clearest form, let us first understan 
what growthis. It appears in all cases to consist in the evolu- 
tion or production of cells from those already existing. Accord- 
ing as the circumstances under which the cells are produced 
vary, so does the tissue ultimately produced vary. Cells fo: 
in woody fibre, become wood. Cells formed in muscle in their 
turn form muscles, but the starting point of the process in every 
instance is the formation of new cells. . 
If now we examine the evolution of cells under the simplest 
conditions, as, for example, in the fermentation that attends the 
manufacture of alcohol, we find that with the evolution of t) 
torulz cells carbonic acid is produced. The two results are 
intimately connected, and it is proper to suppose that since t 
carbonic acid has arisen along with the new cells, the latter 
operation must in some way involve a process of oxidation. 
Accepting the hypothesis that oxidation is attendant on these 
processes of cell growth under the simplest conditions, we p 
to the examination of what occurs in the lowest forms of vege: 
table organisms found in the air. ee 
The fungi, and indeed all plants that are not green, with a few 
exceptions, exhale carbonic acid and never exhale oxygen. 
this case, in which cell production often occurs with such mar- 
yellous rapidity, the carbonic acid must have arisen as a con: 
quent of the cell growth. It is improbable that it has b 
absorbed by roots and exhaled from the structures, either in th 
plants or in those produced during fermentation, In the lal 
there never are any roots, and in the former, even where rot 
are present, they bear a small proportion to the whole pla 
The quantity of moisture exhaled by such growths is also in 
nificant, and out of proportion to the carbonic acid evolved. We 
mus’, therefore, in this case decline to accept the root-absorption 
hypothesis, and admit that the carbonic acid has arisen as a result 
of the cell growth in the plant. j 
Passing to the chlorophyll-bearing plants, we find that in th 
Phanerogamia it is only the green parts that at any time exha 
oxygen, and then only under the influence of sunshine, 
other parts of the plant above the ground, that are not green, 
viz., the stem, twigs, flowers, &c., are at all times, day ant 
night, exhaling carbonic acid. The whole history of the plant, 
from the time the seed is planted, to its death, is a continuo 
story of oxidation, except when sunlight is falling on the leave 
The seed is put into the ground, and during germination oxygel 
is absorbed and carbonic acid exhaled. If the seedling be kept 
in the dark, oxygen is never exhaled, carbonic acid is, and 
plant not only grows, but all visible structures except flo 
are formed in a rudimentary condition. In the light the groy 
during the night time is attended by the evolution of carbo 
acid, while during the day time the bark of the stem d 
branches is throwing off carbonic acid. When flowers and seed 
form, the evolution of carbonic acid attending this highest act | 
which the plant is capable, is often greater than that produced 
at any time in many animals. 
Everything in the history of plants, therefore, tends to shoy 
that the evolution of their structures is inseparably attended bj 
the formation of carbonic acid ; and it seems impossible, whet 
we consider the evolution alone, to arrive at any other opini 
than that already expressed—that, all living things, whet 
plant or animal, absorb oxygen and evolve carbonic acid, 0} 
some other oxidised substance, as an essential condition of th 
evolution of their structures, J. C. DRAPER 
SCIENTIFIC SERIALS 
THE first number of the Zeitschrift fiir Ethnologie for 1873, 
opens with an interesting paper by Dr. George Schweinfurth 
on the Monbutta Tribes of Central Africa, whose name and 
existence have hitherto been unknown to us. Dr. Ori and My 
Jules Poncet had shown that there were important strea' 
south of the Miam-Miam Territory, which took a westerly cour: 
and that the banks of the mest considerable of these rivers w 
