CHAPTER III 



STEMS AND BUDS 



THE stem is that part of the plant which connects the root 

 with the leaves. The most common types of stems of seed- 

 bearing plants are above ground and serve to support the foliage 

 and flowers. They usually show more or less well-defined divi- 

 sions into nodes (joints), and internodes as indicated by 

 branches, leaves and leaf scars, buds and bud scars. (Figs. 20 

 and 21.) They produce branches at the nodes more or less 

 regularly. At the points where the new season's growth begins 

 we find a number of scars very close together. (Fig. 20.) By 

 examining the scars we can usually determine the amount of 

 growth of the twigs for several years past. 



There are two well-defined types of stems, the exogenous 

 (Fig. 22 a), or the outside growing, and the endogenous (Fig. 

 23 a) or inside growing. The former is much more abundant 

 than the latter, and the two can be readily distinguished by cut- 

 ting them in cross sections. In both cases the stems are com- 

 posed of hard, woody bundles surrounded by a softer substance 

 which is covered by the bark or protective covering. The ar- 

 rangement of these bundles is quite different in -the two classes. 

 In the exogenous stems (Fig. 22) the bundles are almost always 

 arranged in a circle and the strength of the stem depends, in 

 a large measure, on their compactness. Such stems will in- 

 crease in diameter as long as the plant is alive and growing. 

 This increase in diameter is due to the formation of a layer 

 of wood just outside the last year's growth of wood. This very 

 thin layer of cells in which the new growth is occurring is 

 known as the cambium. These annual layers are so distinct that 



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