STEM- AND TOP-GROWTH, ETC. 21 



The stem or branches below the one-year-old growth 

 never increase in length. The space between the nodes 

 on a grape-vine or tree depends on the rapidity of growth. 

 In nursery trees the thriftiness of growth can be deter- 

 mined by the purchaser by observing the length of the 

 internodes. "With evergreens, small fruits, and in other 

 cases, it is often a gain to secure more compact growth by 

 pinching the points during the season of active growth. 

 Pinching stops the development of the succeeding node 

 and causes the development and growth of buds farther 

 back on the plant. 



23. General Classes of Stems. — Eoots are annual, bien- 

 nial, or perennial, depending on their length of life. In 

 the same way the stem-growth is divided into two main 

 classes or divisions, the herbaceous stems living only one 

 year, and the woody plants living more than one year, 

 and in some cases one hundred years or more. When of 

 small growth woody plants are classed as shrubs. But it 

 often happens that shrubs in one climate are trees in 

 another, and herbaceous plants in one climate become 

 woody-stemmed trees in another. As an instance, we 

 have seen the castor-oil bean grown into a woody-stemmed 

 tree in Cuba thirty or more feet in height and with a stem, 

 ten inches in diameter. As to mode of cell-growth, our 

 cultivated plants are divided into two main classes or divi- 

 sions, the "exogens" and the "endogens," meaning 

 "outside growers " and " inside growers." Corn, aspar- 

 agus, palms, ferns, and many tropical trees are inside 

 growers or endogens. In this division the new cell-growth 

 is mingled with the older tissue, and growth of the stem 

 is by distension or pressing outward from the inside. 

 This class of stems does not show the bark, wood, and pith 

 of the outside growers. The exogenous division includes 

 all our northern trees. 



