72 THE STORY OF THE PLANTS. 



blossom whenever a warm and sunny spell occurs 

 in January or February. The remaining bushes 

 are covered through the winter with hairy brown 

 buds, and burst out in early spring into golden 

 masses of scented blossom. A like arrangement 

 also occurs in many catkins, which are the flowers 

 of certain trees; the catkins of the birch and the 

 alder, for example, are always formed in early 

 autumn, though they only break into bloom with 

 recurring warmth in March or April. 



We have travelled away so far from our origi- 

 nal question of How plants dtink, that a sum- 

 mary of this chapter is even more necessary than 

 usual. 



Plants drink by means of roots. But they 

 take up by them, not only water, which is their 

 needful solvent, but also other materials urgently 

 required for their growth and development. The 

 most important of these materials is certainly 

 nitrogen, which forms an indispensable compo- 

 nent of protoplasm and chlorophyll. Where, how- 

 ever, the roots do not supply nitrogenous matter 

 in sufficient quantities, plants procure it for them- 

 selves by means of their leaves or stems, and 

 therefore become insect-eSting or flesh-eating. 

 Soils get exhausted at times of nitrates, phos- 

 phates, and other necessary materials of plant- 

 life. The farmer meets this difficulty by manur- 

 ing, and by rotation of crops. Nature meets it 

 by dispersion of seeds. Roots, however, have 

 other functions besides drinking water and suck- 

 ing up with it certain dissolved materials; the 

 chief of these other functions are fixing the plant 

 securely in the ground, and affording a safe place 

 of winter storage for starches and other surplus 



