phyll to hypodemis laiu rron one lon^^itudiricd partition 

 to t]ie next. 



Tliat part of eacli primary partition cell left after 

 the separation of tlie sinr;le cross partition cell at eacli 

 end, dooG not divide further "by iongi uainal tm-i.iclinos, 

 till very much later, "bu immediately gives rise to the 

 longitudinal partition between the adjacent air canals. 

 As tiiese cells grow in a radial direction they are divided 

 by periclines iintil, in the mature leaf, the pa.rtitions 

 may be fifteen cells or more in radial breadth and fon^i 

 one third the diameter of the petiole, but thby are only 

 one cell thick (L.p^ Fig, IS, 20). Tliese cells grow with 

 the longitudinal gro¥/th of the letif (Figs. 21 - 21-). As 

 each cell elongates it is seen that the primary cross par- 

 tition cell at one end (c.p.c.^Fig. 22) is nearer the 

 acroscopic v/all of the longitudinal partition cell, and at 

 the other end is nearer the basiscopic v/all. Then wlien the 

 transverse anticline appears it is somet^hat oblique, and 

 thus forms two wedge shaped c lis, each with a cross par- 

 tition cell at the broad end and none at the narrow one 

 (Fig. 23). The cross partitions in adjacent air canals are 

 tlius not opposite but alternate. These wedge shaped cells 

 continue to grow and divide frequently by transverse anti- 

 clines, till in the matLire petiole the cross partitions arc 

 far apart. Heru xu uhe longitudinal partitions also v/e 



