168 



HUTCHINSON'S POPULAR BOTANY 



first. Meanwhile, the root-fibres (which are really adventitious roots pro- 

 ceeding from the base of the plumule) continue to grow, taking a down- 

 ward direction, while the stem begins to force its way towards the light 

 and sun Why the stem should take an upward course, contrary to the 

 force of gravity, is not known, but the fact is interesting. Our ignorance 

 of the ultimate causes of many other occurrences quite as common is not 

 less complete. Why are fluids incapable of resisting a change of shape ? 

 We cannot tell. Why does the earth attract the 

 bodies on its surface, or the sun attract the earth ? 

 Still we are at a loss. We are familiar with facts, 

 and are able to deduce what are called physical laws 

 from them, but of the ultimate causes of the phe- 

 nomena themselves we know nothing. 



On removing a germinating grain of Barley from 

 the ground, the young stem will be found to be sur- 

 rounded at its base by a sheath (fig. 210 1. which is 

 called the seed-leaf or cotyledon, and which should 

 be particularly noticed. We shall refer to it again 

 in a moment. The grain contains starch and gluten, 

 and remains for some days adhering to the base of 

 the young plant a reservoir of nutriment. As 

 growth proceeds this food supply diminishes, being 

 conveyed to the seedling and used by it for evolv- 

 ing new protoplasm and cell-walls : nor is germina- 

 tion, properly speaking, at an end till the whole is 

 used up, and the empty husk loosens from the plant. 

 The proportions of starch and gluten (gluten, it 

 should be remembered, is one of the proteids) vary 

 in the different kinds of plants of the Grass order 

 (Wheat. Rice, Maize, Millet, etc.), and on these rela- 

 tive proportions depend the alimentary properties 

 of the various cereals. 



Similar in some respects to the germination of 

 Barley, though strikingly dissimilar in others, is the 

 germination of a bean (figs. 212-14). In this case a 

 primary root, formed by the direct growth and 

 elongation of the embr\-o root or radicle, strikes 

 down into the earth, and gives off lateral branches or secondary roots, 

 which in their turn may send out a third series of branches, and so on 

 (fig. 213). Meanwhile, the plumule or young stem, with its bent, yellow- 

 green tuft, elevates itself above the soil, and straightens as it rises ; while 

 the tuft itself, expanding under the influence of solar light and heat, is 

 seen to consist of two perfectly formed leaves the first foliage leaves of 

 the plant. Until these leaves are able to take in food from the atmosphere 



FIG. 206. FRUCTIFICA- 

 TION OF A MOSS-PLANT 

 (Polytrichum gracile), 



In section, showing the two 



loeuK, or spaces, filled with 



spores. 



