722 
CHEMICAL PROCESSES IN THE PLANT. 
but if this happens only for a short time the motility returns when the oxygen is 
again restored. 
The respiration of plants is, like that of animals, associated with a loss of 
assimilated substance, this loss being always a great deal smaller in assimilating 
plants than the gain of substance by the activity under the influence of light of 
the cells which contain chlorophyll ; but when, as in the germination of seeds, an 
energetic growth is combined with powerful respiration, no new products of as- 
similation replacing the loss, the loss in weight of the growing plant may be very 
considerable. Seeds which germinate in the dark may in this way lose almost 
one-half of their dry weight, and it would seem that this loss is occasioned ex- 
clusively by the decomposition of the non-nitrogenous reserve material^ and its 
combustion into carbon dioxide and water. If the non-nitrogenous reserve-material 
consists of oil, e. of a substance containing very little oxygen, a portion of the 
inhaled oxygen remains in the germinating plant, carbo-hydrates containing a large 
quantity of oxygen such as starch and sugar being formed at the expense of 
the oil. 
The loss of assimilated substance caused by respiration would appear purpose- 
less if we had only to do with the accumulation of assimilated products ; but these 
are themselves produced only for the purposes of growth and of all the changes 
connected with life ; the whole life of the plant consists in complicated movements 
of molecules and atoms ; and the forces necessary for these movements are set 
free by respiration. The oxygen, while decomposing part of the assimilated sub- 
stance, sets up important chemical changes in the remaining portion, which on their 
part give rise to diffusion-currents, and these bring into contact substances which 
again act chemically on one another, and so on. The dependence on respiration of 
the movements in protoplasm and motile leaves is very evident, since, as has been 
mentioned, they lose their motility when oxygen is withheld from them. These 
considerations lead to the conclusion that the respiration of plants has the same 
essential significance as that of animals ; the chemical equilibrium of the substances 
is being continually disturbed by it, and the internal movements maintained which 
make up the life of the plant. Respiration is, it is true, a source of loss of sub- 
stance ; but it is also in addition the perpetual source from which flow the forces 
necessary to the internal movements ^. ' 
^ [According to Borodin (Ueb. die physiol. Bedeutung des Asparagins im Pflanzenreiche, Bot, 
Zeitg. 1878) this is not the case. In the process of respiration the nitrogenous substances constituting 
the protoplasm become oxidised, and of this oxidation asparagin is one of the products. The non- 
nitrogenous materials are used up in supplying plastic material to the protoplasm. 
Asparagin is regarded, from this point of view, as a nitrogenous waste- product (metabolite), and 
it therefore corresponds physiologically to the urea formed in the animal body, a comparison which 
was long ago suggested by Boussingault.] 
^ [M. Corenwinder, from a series of observations on the Maple and Lilac, has confirmed the 
view to a certain extent held by Mohl, that the process of respiration is always going on in a plant 
even when concealed by the greater activity of the decomposition of the carbon dioxide by the 
parts containing chlorophyll. He distinguishes two periods in the vegetative season of the plant : — 
the first period, when nitrogenous constituents predominate, is that during which respiration is most 
active ; the second, when the proportion of carbonaceous substance is relatively larger, is the period 
when respiration is comparatively feeble, the carbon dioxide evolved being again almost entirely 
taken up by the chlorophyll, decomposed, and the carbon fixed in the process of assimilation. He 
