240 



THE MAINTENANCE OF THE INDIVIDUAL 



e e i 



regions several different methods of growth occur which will be 

 described later. Some plants that grow more or less continuously, 

 forming a woody body which resists cold and storm, are called trees 

 or shrubs. Others die down at the end of the year, although they 

 have some wood fiber in the body. These are the herbaceous plants, 

 examples of which are peas, beans, and a variety of garden plants and 



roadside weeds. Herbaceous plants 

 DiCotyledoiv MoaocotyledoR that produce seeds and die before 



the following winter are called 

 annuals. 



A second group of herbaceous 

 plants, called biennials, store food 

 in the roots or underground portion 

 of the stem. After the upper part 

 of such a plant is cut down by un- 

 favorable weather conditions, the 

 following spring the underground 

 portions send up a new shoot from 

 the subterranean food supply. This 

 gives rise to flowers and seeds at 

 the close of the second year. Ex- 

 amples of biennials are carrots, 

 parsnips, and beets. 



A third type of herbaceous plants 

 is the perennial, which grows each 

 spring from the underground parts 

 that remain alive during the winter. 

 Many of our common weeds have 

 this habit, which makes them 

 difficult to eradicate. 



Woody plants, such as trees and 

 shrubs, as we have seen in the 

 unit on classification, are grouped either as conifers (the softwoods, 

 pines, firs, hemlocks, and their relatives) or as deciduous hardwoods. 

 The latter are placed with the flowering plants, and may be either 

 monocotyledons or dicotyledons. These two groups have differences 

 in the structure of leaf, stem, and seed. The monocotyledons usu- 

 ally have parallel-veined leaves, like those of grass or lily. Their 

 stems have scattered "closed" woody vascular bundles and a single 

 cotyledon in the seed. The dicotyledons have netted-veined leaves, 



iS tern 



Differences between monocoty- 

 ledons and dicotyledons; c, cotyle- 

 don ; e, endosperm ; fb, fibrovascular 

 bundles; h, hypocotyl; p, plumule. 



