32 



STEMS AND BUDS 



they can be readily seen on the cut ends of tree trunks, with the 

 naked eye, and are known as annual rings. (Fig. 24.) All the 

 dicotyledonous and coniferous jjlants have stems of this type. 

 If you cut a cross-section of a soft, rapidly growing stem (be- 

 gonia or geranium), you can see these bun- 

 dles more or less well defined. If you cut 

 a cross-section of a woody stem, you will 

 readily recognize these bundles which are sep- 

 arated by radiating lines. 



We find two types of endogenous stems. 

 One which consists of a mass of soft, pithy 

 tissue surrounded by a hard rind and con- 

 taining scattered, woody strings known as 

 fibro-vascular bundles (Fig. 23), and an- 

 other which is of the same general character, 

 but is hollow, and therefore the fibro-vascular 

 bundles are forced into the form of a cyl- 

 inder. All of the grass stems are endogen- 

 ous; the corn which is a coarse grass, is a 

 good example of the first type and the various 

 grains and most common grasses are exam- 

 ples of the second type. These fibro-vascu- 

 lar bundles or woody strings can be readily 

 recognized in the corn stalk. 



Stems in which the fibrous bundles are 

 small as compared witH the surrounding ma- 

 terials are soft and juicy, and are called 

 herbaceous^ while those in which the bundles 

 constitute the gi-eater part of the substance 

 are called ivondy. Most of the strictly woody 

 plants have exogenous stems and show rings. (Chapter VIII.) 

 Stems Above Ground. — The aerial, or above-ground, stems; 

 may be very short as in the case of the turnip or radish, in which 



FiQ. 20.— a, maple 

 twig showing buds, leaf 

 scar and annual growth ; 

 b, horse chestnut twig 

 showing same. 



