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44 THE GROWTH AND PARTS OF PLANTS 
but the short stem under ground, or at the surface of 
the ground, lives on from year to year. When the 
seed germinates, the plant 1s so small at first, and even 
for several seasons, that for the first few years no flow- 
ers and seed are formed. ‘Those herbs which live for 
several years, as well as the trees and the shrubs, we 
call perennial plants. In these plants, also, so far as 
we know, the main purpose of the plant, from the 
plant’s point of view, 1s to form seed and perpetuate its 
kind. Plants like the cotton, castor-oil bean, etc., are 
perennial in the tropics but become annual in temperate 
zones, because the cold weather kills them; they pro- 
duce one crop of seed the first season. 
Woody plants and herbaceous plants. The stems and 
roots of trees and shrubs are mostly of a hard substance 
which we call wood. They are often called woody 
plants, while the herbs, whether annual, biennial, or 
perennial, are herbaceous plants. 
