GERMINATION. 
every possible precaution to ensure the equality of 
moisture in both situations, he constantly found the 
seeds in the shade germinate sooner than those in the 
light“. We may, conclude, therefore, that light is in 
jurious to germination ; and hence one reason for cover 
ing seeds with the soil in which they are to grow. 
7. Thus we have seen that seeds will not germinate 
unless moisture, beat, and oxygen gas be present; and 
that they do not germinate well if they are exposed to 
the action of light. Now, in what manner do these 
substances affect the seed? What are the changes which 
they produce? 
It was observed before, that all seeds have one or 
more cotyledons. These cotyledons contain a quantity 
of farinaceous matter, laid up on purpose to supply the 
embryo plant with food as soon as it begins to require 
it. This food, however, must undergo some previous 
preparation, before it can be applied by the plant to the 
formation or completion of its organs. Now all the 
phenomena of germination, which we can perceive, con 
sist in the chemical changes which are produced in that 
food, and the consequent developement of the organs of 
the plant. 
When a seed is placed in favourable circumstances, 
it gradually imbibes moisture, and very soon after emits 
a quantity of carbonic acid gas, even though no oxy 
gen gas be presentt. If no oxygen gas be present, the 
process stops here, and no germination takes place. But 
if oxygen gas be present, it is gradually absorbed by the 
seed ; and at the same time the farina of the cotyledons 
* Encyc. Metb. Physiol. Veget. 126. 
1 Sough, Minch. Mem. iv. 315.— Cruikshank, Rollo on Diabeter, p. 452. 
157 
Chap. II. 
Phenomena 
of germina 
tion. 
Torsedans 
prepare 
food,