62 EASY LESSONS IN VEGETABLE BIOLOGY. 



circles of fibro- vascular bundles, with cellular rays 

 passing from the pith to the bark. Chap. VI, Sees. 

 9, 10. These circles are supposed to indicate the layers 

 of annual growth, but this is quite uncertain. Some- 

 times two or more circles are formed in a year. The 

 diameter and height attained by some E^xogens may 

 be very great. The Big-Tree Grove, in Calaveras 

 County, California, contains trees from 350 to 400 

 feet high, and 33 feet in diameter. 



The stems of Endogens, or inside-growers, exhibit 

 in their sections no distinct pith, no concentric circles, 

 no medullary rays, and no separable bark. 



7. Stems produce buds, which may be regarded as 

 shortened axes, capable of elongation. According to 

 the organs which result from their development, they 

 are termed stem-buds, leaf -buds, and floiver-buds. 

 They are terminal if produced at the extremity of 

 the primary axis, and lateral if at the sides of the 

 axis. In palms and tree-ferns the bufls are termi- 

 nal, and if the top of the stem is cut off the 

 plants perish. Buds are often protected by coarse 

 leaves or scales, which may be covered with hairs, 

 or with gummy or resinous matter for additional pro- 

 tection. 



Buds often lie dormant, and do not appear as 

 branches unless stimulated by some local injury to the 

 plant ; others are altered into thorns. Thorns are 

 undeveloped branches, and many plants which are 



