THE RELATION OF THE PLANT TO THE AIR 181 
When the starch is made in the leaf it is changed into 
sugar, and in this form is distributed through the plant, 
passing especially to the seeds and tubers, where it is recon- 
verted into starch and stored up. It must be remembered 
that although seeds, bulbs, and tubers contain plenty of starch, 
they do not make it in the first instance: they are the chief 
storehouses of the plant. Thus, if the leaves of Snowdrops 
are cut off as soon as the plant has flowered, the next year’s 
corm is not formed, owing to its not having received food 
through the leaves. 
The making of starch from carbon dioxide and water is 
commonly spoken of as assimilation, but this is only one of 
many instances of the building up of substances that is con- 
stantly going on in the plant. 
COMPARISON OF THE PROCESSES OF RESPIRATION 
AND ASSIMILATION. 
RESPIRATION. Ge ASSIMILATION. 
1. Carbon dioxide given off. 1. Carbon dioxide taken in. 
2. Oxygen taken in. 2. Oxygen given out. 
3. Goes onin all parts of the 3. Goes on in green parts of 
plant, and at all times. the plant, and onlyin sun- 
light. ue 
4. Aprecesscommonto plants 4. Takes placein plants alone, 
and animals alike. and only under certain 
conditions. — 
