138 



PLANT LIFE. 



of the blade, its tissues are produced. In sucli plants apical 

 growth ceases so early that it can 

 he observed only in the youngest 

 stages. 



170. Of branched leaves. — 

 When the leaf is to become niiK li 

 branched, two or more new growing- 

 l)oints develop, so that each of the 

 branches has at its apex a growing- 

 point (fig. i66). These growing- 

 points may arise from the a]iical 

 growing-point, or from the basal 

 one, or sometimes from both. The 

 .. ..^ liranches will appear accordingly 



Fig. ,f,<;^E„dmEnfavei.iin the !« acropctal or basijictal succcssion, 

 ^r^'i^^kii-dcdi/'oF';!;: or even in both as they do in the 



xvlem ; c. c. inesophvH cells with i r nM i ■ -j r .1, 



cfiioroplasts ; ,., l cells of the leaves of yaiTow. 1 he limits of the 

 -l^ttrTrank''"'""''''' '"'*""■ gro wi ng-i.)oi ut are even more in- 

 definite than in the stem. The cells of which tlie leaf is 

 composed are produced very rapidly, and at a very early 

 stage division ceases. 



171. Wintering. — In those plants which live from year to 

 year, producing new lea\es each spring, the unfolding of 

 these from the winter buds is due chielly to the enlargement 

 of cells already formed. New lea\'es are ordinarily produced 

 before the close of the growing season preceding that in 

 which they are expanded, and are protected in the winter 

 buds. The partly develojied leaves in the bud may be Hat, 

 but broad leaves arc commonly folded or rolled in various 

 ways. 



172. Growth limited. — The growth of the leaves is ordi- 

 narily limited, rareh' extending o\er a single season. In a few 

 ferns and coniferotis plants the lea\es continue to gro\\' for a 

 longer time. Indeed, in the curious Wclwitschia (ilg. 167), 



