BOTANICAL TERMS. 



Stinging hairs secrete a poisonous liquid. The point 

 of a hair of this kind on piercing the skin breaks off, 

 leaving the poison in the wound. 



Prickles (Fig. 249) differ from tJiarns in being out- 

 growths of the bark • thorns arise from the wood. 



GROWTH. 



The growth of a plant consists in the multiplication of its cells, 

 and the subsequent enlargement of the latter by the addi- 

 tion of new matter. The development of the cell frequently- 

 involves, also, a change of form. 



Grermination. 



By this term is meant the commencement of tlie process of 

 growth from the seed. Under suitable conditions of 

 temperature and moisture the einbrj'o, which is dormant 

 in the dry seed, wakens into activity and begins to 

 develope. The details of the process var\- somewhat 

 according to the structure of the seed. If the cotj'ledons 

 are thin and leaf-like, as in Maple for example, the radi- 

 cle generally grows throughout its length so as to raise 

 them above the soil, where they at once expand and 

 become the first green leaves of the new plant, a root 

 being at the same time developed from the lower end of 

 the radicle. But if the cotyledons are thick and flesh}-, 

 containing much nourishment, then usuallj'^ a bud called 

 the plumule, which contains the elements of additional 

 bits of stem, will be a prominent feature in the embryo, 

 and in this case the cotj'ledon or cot3-ledons not infre- 

 quently remain under ground, as in the pea and the 

 acorn, and so do not perform tlie office of foliage-leaves, 

 but merely suppl\' the newl}- developing parts witli nour- 

 ishment. In albiiminous seeds, the endosperm is the 

 chief source from which the germinating embrj'o derives 

 its support. 



Vitality of Seeds 



There is a considerable difference in regard to tlie length of 

 time during which seeds retain their vitality. Some, 

 such as those of Elm and Poplar, will gei-minate only 

 if they have been kept fresh and not permitted to dry 

 up, while others, such as those of Indian Corn and 

 Wheat, and in general those containing a copious store of 

 starch, maj- be kept for a verj' long time without losing 

 their germinating power. 



