WOODY PLANTS AND HERBACEOUS PLANTS 255 



of conjugation of the gametes, is thus rendered quite 

 independent of external water, and the gametes are 

 withdrawn from the danger of desiccation. The 

 fertilised egg also germinates inside the megaspore, 

 where it produces the embryo, which develops up to 

 a certain point and then enters upon a resting stage. 

 The ovule (megasporangium) containing the resting 

 embryo, together with a store of food providing for 

 the development of the embryo into the free-living 

 plant, is called the seed. Here then not only the sexual 

 generation, but also the early stages of the new individual 

 developed from the fertilised egg are produced within 

 the body and nourished at the expense of the parent 

 sporophyte. 



The hundreds of thousands of existing species of 

 Seed Plants are exceedingly various in form and life 

 history. We can only consider a few of the general 

 types into which these can be grouped. 



First, a broad distinction, though by no means an 

 absolute distinction, can be drawn between woody 

 plants and herbaceous plants. The subaerial shoots 

 of woody plants (trees and shrubs) persist from 

 year to year, and constantly form new portions of 

 the shoot system which are continuations of the portions 

 already formed. At the same time the parts already 

 formed in most cases grow continuously in thickness, 

 and the new layers so added are mainly composed 

 of hard woody tissue. Thus the whole plant body 

 constantly increases in size. 



In the herbaceous plant, on the other hand, the 

 subaerial shoot consists mainly of soft tissue and is 

 short-lived, generally dying down after one growing 

 season. The whole vegetative plant may die after 

 one season's growth, when its seeds have ripened 



