Germination. 557 
seed may be. This is soon followed by the appearance of 
the plumule or growing point of the stem, emerging from 
between the cotyledons when there are two, or laterally when 
there is only one.’ Immediately water is absorbed, and, other con- 
ditions being favourable, important chemical changes are started 
into operation. The most important is the transformation of 
the insoluble starch of the perisperm or cotyledons into soluble 
sugar, thereby rendering it available to circulate with the 
imbibed water in the growing tissue. This constitutes the first 
food of the young plant, just as milk is the first nourishment 
of the young of mammiferous animals, and the white of an egg 
thé support of the young bird during the period of incubation. 
The solution of the starch is gradual in its action, and, when 
this provision is exhausted, if due care has been taken in the 
selection of soil and in the supply of moisture, the young plant 
will be in a state to draw and to assimilate the elements it 
requires from the earth. In by far the greater number of 
plants the cotyledons are borne above the soil, as in the Scarlet 
Runner Bean ; but there are others, like the Pea, in which they 
remain buried in the ground. And, again, there are others 
in which the cotyledon or cotyledons never become free from 
the seed-shell, especially of those seeds of which the albumen 
is of a horny nature, and in which the process of conversion 
into sugar is slow; the cotyledons serving in this case as con- 
ductors of the sugary matter to the young plant, according as 
it is developed from the albumen. So long as the cotyledons 
remain buried beneath the soil, they retain the white hue they 
had in the seed; but as soon as they are brought under the 
influence of light, they secrete chlorophyll, and otherwise fulfil 
the functions of true leaves. 
The time consumed by seeds in germination varies according 
as the conditions are more or less favourable for the same 
species; but there is a greater difference in the time required 
by the seeds of different species. Certain seeds, those of the 
common Mustard (Sinapis alba) amongst others, will germinate 
in forty-eight hours, or even in a shorter period ; whilst the 
majority of seeds require a week, and from that to several weeks. 
And lastly, there are some seeds that exhibit no sign of life 
until they have been in the ground one or two years. These 
1 The germination of Ferns, as explained under that order, is a very different 
process; the act of impregnation not taking place till after the first stage of 
development of the spores. 
