264 Organic Physics. [March, 
nection. Fats frequently appear in the plant cells, but starch, 
which occurs in limited quantities in animal cells, is the most 
abundant constituent of those of plants, and the mode of its 
occurrence is specially interesting. Whatever be the true process 
of carbon assimilation in the leaves, the fact that the starch pro- 
duct makes its appearance in the interior of cells, and that there 
is a chemical reduction of the cell protoplasm, is very important, 
Starch is not directly produced by the union of carbon with some 
sap molecule, but is apparently the result of some special cell 
metamorphosis, and on the character of this metamorphosis much 
light is thrown by Pringsheim’s late researches into the nature 
and changes of chlorophyll. 
The fact that assimilation takes place only in sunlight is pat- 
ticularly interesting in its bearing on the preceding hypothesis. 
We seein to have here a special case of contact influence. It is 
known that plants respire oxygen day and ‘night. This oxygen 
is mainly employed in the plant interior in yielding force in aid of 
nutrition. But in the leaves it is otherwise employed, and here 
we have distinctive waking and sleeping periods. In the dark the | 
whole plant sleeps; nutrition alone goes on. In the light the 
leaves awake ; tissue oxidation is setup. It would appear, then, 
as if the contact or vibratory influence of the light rays was the 
agency which set up this special oxidation of protoplasm. 
Pringsheim has shown that if the light be very intense the i 
oxidation grows so vigorous as to destroy the cells. If there be 
no light there are no oxidation products. The admission of 
light yields chlorophyll as its first resultant, this green coloring 
matter henceforth acting as a protective screen to the cell against 
the too vigorous action of the light rays. A somewhat later m : 
duct is the readily oxidizable substance which he names hyp% 
chlorin. oa 
These changes are appearently preliminary to the assimilation 
of carbon. The character of the subsequent changes is not Y d 
evident. The respired oxygen apparently effects a reduction 
the hypochlorin to a lower stage, and may possibly set 
molecule having a vigorous affinity for carbon, sufficient tow 
come its affinity for oxygen, and thus to decompose the pee : 
acid molecule. However this be, one thing is certain: the 0 
dation that takes place yields a quantity of free energy. +% a 
light which instigates oxidation, also yields, perhaps as VO" 
