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lliem. The figure and size of the seed depend chiefly u])on the 
cotyledons. This is evidently the case with the bean, and it is so 
with all other seeds. The number of cotyledons is different in 
different seeds. Some seeds have only one cotyledon, as the 
seeds of wheat, oat, barley, and the whole tribe of grasses ; but 
most seeds, like the bean, have two cotyledons. 
When a seed is placed in a situation favourable to vegetation 
it very soon changes its appearance. The radicle is converted 
into a root, and sinks into the earth, the plumula on the other 
hand, rises above the earth, and becomes the trunk or stem. 
AVhen these changes take place, the seed is said to germinate : 
the process itself has been called germination. Seeds do not 
germinate equally and indifferently in all places and seasons. 
Germination, therefore, is a process which does not depend 
upon the seed alone ; something external must also affect it. 
It is a well known fact, that seeds will not germinate unless 
moisture have access to them ; for seeds, if they are kept per- 
fectly dry, never vegetate at all, and yet their power of vegeta- 
tion is not destroyed. AVater, then, is essential to germination. 
Too much water, however, is no less prejudicial to most seeds 
than none at all. The seeds of water plants, indeed, germinate 
and vegetate extremely well in water ; but most other seeds, if 
they are kept in water beyond a certain time, are rotted and 
destroyed altogether. 
It is well known also, that seeds will not germinate, even 
though supplied with water, provided the temperature be below 
a certain degree. No seed, for instance, on which the experi- 
ment has been tried, can be made to vegetate at or below the 
freezing point : yet this degree of cold does not injure the veg- 
etating power of seeds; for many seeds will vegetate as well as 
ever after having been frozen, or after having been kept in fro- 
zen water. AVe may conclude, then, that a certain degree of 
heat is necessary for the germination of seeds : and every spe- 
cies of plant seems to have a degree peculiar to itself, at which 
its seeds begin to germinate; for every seed has a peculiar sea- 
son at which it begins to germinate, and this season varies with 
the temperature of the air. Mr. Adanson found that seeds, 
when sown at the same time in France and in Senegal, always 
appeared sooner above ground in the latter country, where the 
climate is hotter than in France. 
