1908] 



DORETY—CERATOZAMIA 



213 



Other changes occur as the meriphyte ascends the petiole (c, d). 

 Just below the first pair of pinnae the branching is rapid, and at the 

 level where the blade is seen exteriorly to separate from the petiole, 

 there are four strands provided for it (j). In the rachis another 

 approximation takes place (/), and the number of bundles is reduced to 

 two (m). Each enters a pinna and branches continuously (n, 0). 

 The growing point terminating the rachis has no vascular trace 

 in this leaf, in this respect agreeing with the young leaf represented in 

 fig. 10a. As the plant increases in age, the meristem of this point 

 retains its activity longer, producing a greater number of pinnae, as in 

 the seed plants. 



The wood in all the leaf traces is endarch in the central cylinder 

 (fig. 26), but it soon 

 becomes mesarch, with 

 the protoxylem mov- 

 ing outward by almost 

 imperceptible degrees. 

 It never reaches the 

 exarch condition, how- 

 ever; even in the tips 

 of the pinnae there are 

 always two or three 

 elements of centrifugal 

 wood. Here and there 

 may be seen a few 

 elements of transfusion tissue. 



Mucilage canals are numerous in the leaf bases (figs, jo, 31), 

 but they have no more definite arrangement there than in the 

 base of the cotyledon. Throughout the region of the stipules 

 there is a gradual decrease in number, which is not altogether 

 due to fusing. Toward the upper levels of this region they are some- 

 times arranged in two series, an adaxial row and an abaxial one, 

 with a definite relation to the bundles (text fig. 2b). About i cm 

 above the base, there is left only one centrally located canal (d), 

 which persists for half the length of the petiole (e). 



The bases of the leaves as well as of the cotyledons are covered by a 

 thick layer of cork. As was seen externally, the hypocotyl is extremely 



Fig. 2. — Cross-section of flattened cells from inner 

 face of petiole near the base. 



