i88 TEXTBOOK OF BOTANY 



in time ceases to grow and straightens itself as much as pos- 

 sible, it is brought close against the supporting object. 

 Therefore, the older parts of the stem are wound tightly about 

 the support, but the younger part, including the intemodes 

 that are still growing, is loosely wound. 



208. Stems of Different Forms. — There are many differ- 

 ent kinds or species of seed plants which differ greatly in their 

 ability to live and grow in different sorts of places. Some 

 plants, such as the dandelion, have spread into many re- 

 gions and many countries. But each kind of plant, never- 

 theless, can live only under a certain range of conditions, and 

 as a rule this range is rather narrow. A plant that naturally 

 grows on dry land will not usually live long if transplanted to 

 a swamp ; a tropical plant will not endure a cold climate. 

 This means that each species is adapted to certain conditions 

 of life ; and different plants are adapted to different conditions 

 by the different ways in which they are built up. Since 

 various seed plants live under so many varying conditions — 

 in warm climates and in cold, in wet regions and in dry, 

 on the soil, in the water, and perched high in the air upon other 

 plants — it is not surprising to find great differences in the 

 make-up of their stems as well as of their other parts. It is 

 impossible here to speak of all the different forms of stems 

 that seed plants possess ; but some of the more common ones 

 will be mentioned. 



209. Herbaceous and Woody Stems. — Most of the 

 smaller seed plants, especially those that live through but one 

 growing season, have soft stems ; this is because they contain 

 comparatively Httle wood or other thick-walled tissues. 

 Such plants are called herhs. The stems of other plants, par- 

 ticularly of those that live longer and grow to a large size, 

 contain more wood and often a large proportion of other thick- 

 walled tissues as well. Such stems are comparatively hard, 

 and the plants to which they belong are called woody plants. 

 A woody plant with an upright main stem that grows to a 



