Germination. 557 



soed 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. 1 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 

 the 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 Tinder 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 Jmve 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. 



