86 SIR J. LUBBOCK —PHYTOBIOLOGICAL OBSERVATIONS. 
dots, cannot retain its origi nal form of lamina, because it is stopped 
by want of space along the line a, which it will therefore follow, 
as shown in fig. 176. Moreover, the thickened rib or vein (figs. 
171 & 174) will be arrested sooner than the thinner lamina. When 
Fig. 171. 
Fig. 172. 
x 20 
Fig. 171. Liriodendron. Position of young leaf in bud. x12. 
Fig. 172. Ditto. Very young leaf and stipule. X 20. 
Fig. 173. Ditto. Ditto. Second stage. 
Fig. 174. Ditto. Young leaf and stipule in a rather more advanced stage. 
stopped by meeting the stipule, it bifurcates ; and this perhaps is 
one reason why the leaf permanently retains the form which it 
is thus compelled to assume. The lamina grows for a while 
somewhat more rapidly than the stipule, then the stipule more 
