[Chap. XXVII GENERAL REGIONS AND PROCESSES IN STEMS 



Fig. 



100. The Joshvia tree, an arborescent yucca, in bloom. Mojave Desert near 

 Kramer, Calif. Photo bv U. S. Forest Service. 



most prominent tissue. At the extreme tip only parenchyma is present 

 ( Fig. 32, page 69 ) . We have aheady seen ( Chapter XXIII ) how such 

 external factors as light and gravity may influence the direction of growth 

 of an elongating stem tip. To see the growing tip of a grass stem one 

 must first carefully remove the ensheathing leaves. Unless the plant is 

 very young the stem tip will be bearing rudimentary flowers entirely 

 hidden within the leaf sheaths. As the grass stem grows, the bases of the 

 internodes are the last parts of the stem to stop elongating and become 

 mature. 



Size of stems. The forerunner of the whole stem system of a plant is 

 the apical meristem in the bud (plumule) of the embryo (Fig. 8, page 

 11). Through the formation and enlargement of cells in this apical 

 meristem the stem elongates and axillary buds develop from cortical and 

 epidermal cells along its sides. From some of these axillary buds lateral 

 branches develop, each of which also has an apical meristem. 



Although there are seasonal periods of growth and dormancy, it might 



