io6 BOTANY AND PHARMACOGNOSY. 



tive substances from the soil. The subterranean shoots are 

 generally destitute of true leaves and are furnished only with 

 membranous or sometimes thick, fleshy leaves which are bladeless, 

 pale, scale-like or tubular. 



Depending- upon the duration of the shoot (or better the stem), 

 plants are divided into herbs, shrubs and trees. In herbs the 

 aerial shoots are herbaceous, while in shrubs and trees they be- 

 come woody and persist throughout many years. 



J\Iany of the herbs have subterranean shoots, but these are 

 generally absent from woody plants, excepting in Sambucus, 

 Ailanthus, Calycanthus, etc. The herbs may be further sub- 

 divided as annual, biennial and perennial. 



In ANNUAL herbs the individual possesses only aerial shoots 

 and the plant sets fruit the same year that the individual has de- 

 veloped from the seed. In biennial herbs the plant does not 

 produce flowers until the second season. The perennial herbs 

 on the other hand develop flowers continuously for many (or at 

 least several) years and also produce subterranean shoots, such 

 as creeping rhizomes, tubers, bulbs, etc. 



The roots, of annuals, biennials and perennials dififer in a num- 

 ber of particulars. In the annuals, belonging to the monocoty- 

 ledons, the roots are fibrous, possessing numerous lateral branches, 

 whereas in the annuals belonging to the dicotyledons only the 

 primarv roots develop. The biennials are nearly all dicotyledons 

 and have a persistent primary root which while usually slender 

 may become fleshy, as in Beta. In the perennials, on the other 

 hand, we find a number of dififerent types of roots varying from 

 the slender aerial roots of epiphytes, to the smaller tuberous, 

 fleshy roots of many terrestrial plants, and the peculiar roots of 

 parasites. 



III. THE LEAF. 



Leaves are lateral formations upon the stem and their growth 

 is definite. They never occur on other portions of the plant than 

 stems from the surface of which they are developed. Leaves 

 appear in acropetal succession, so that the youngest leaves occur 

 nearest the apex of the stem. Terminal leaves are extremely 

 rare but arise in some instances from the flowers of certain 

 Euphorbiaceai. 



