THE PLANT AND ITS FOOD 28 
product, but it is so rapidly changed to a 
more complex molecule that only very minute 
quantities of it are present at any given instant. 
Such a rapid change would indeed be antici- 
pated, as formaldehyde, even in small quan- 
tities, is a violent poison, that is, it speedily 
reacts with ordinary protoplasm in such a way 
as to destroy the intimate chemical archi- 
tecture of the living substances. The mere 
fact of its poisonous character constitutes 
no objection to its occurring as an inter- 
mediate substance in the synthetic process; 
we know of many other compounds which, 
though deadly poisons under certain circum- 
stances, are still normally present in various 
phases of the transmutation of substances 
going on within the plant or animal body. 
Inasmuch as this synthesis of sugar, by 
means of the chloroplast, is normally dependent 
on suitable illumination, the process is com- 
monly called Photosynthesis,1 a much better 
term than the older expression, Carbon assi- 
milation, by which it was formerly known. 
Since Chlamydomonas is a motile organism, 
it can and does move through the water in 
which it lives in such a way as to become 
exposed to the best conditions of illumination. 
This faculty of taking up a suitable position 
1 Even Photosynthesis is not an altogether satisfactory 
term, for there are strong reasons for believing that 
although light starts the process, it is not concerned in 
the further synthetic processes that result in the formation 
of sugars, 
