NTR0DUCT10N. 



23 



Fig. 13. 



themselves with those of previous for- 

 mation. In this way the external part 

 of the stem becomes very hard, both 

 by this interlacement and from the 

 pressure from within. The whole is 

 enclosed in an integument, which is 

 unlike the bark of an exogen, in not 

 increasing by layers and in not being 

 separable from the tissue beneath. In 

 this stem, although containing the 

 same elements as in that of an exo- 

 gen, the arrangement is widely dif- 

 ferent, the cellular tissue and woody 

 fibre being intermingled throughout 

 the whole diameter. In many cases 

 the stem of an endogen grows by a 

 terminal bud only, as in the palms, 

 and hence is nearly cylindrical. When Sections of stem of Endogen. 



ii i • • • Spiral vessels, c Dotted due 



lateral buds are developed, it is coni- 

 cal, as in Asparagus, &c. 



Buds are undeveloped branches or terminations of stems, covered with the 

 rudiments of leaves. The stem commences from a bud, and is always ter- 

 minated by one. In cold or temperate climates, during the winter, the buds 

 are covered close by overlapping scales as a protection from the severity of 

 the weather. These scales are merely rudimentary leaves. In warm climates, 

 buds are not provided with this defence. All buds are terminal or axillary, 



& 1? 1? & 1? 



a Cellular tissue, 

 lucts. d Woody fibre. 



Fig. 14. 



Fig. 15. 



Bryophyllum Calycinum. 



Leaf bud. a a Marks of 

 attachment of former 

 leaves. 



and hence the arrangement of branches depends upon their peculiar disposi- 

 tion. If the buds are alternate, the branches will likewise be so; if they be 

 opposite, the branches vyill also be opposite. Irregular or adventitious buds 

 are sometimes produced from the root or from the stem, especially if the bark 

 be wounded — or they may even arise from the surface or margins of leaves, 

 as in the Bryophyllum. 



