320 
Harriet E. Allison. 
that in the genus Platycerium there is a progression from a 
comparatively simple type to a more complicated one. In 
P. alcicorne and P. Willinckii, the vascular system is a much 
perforated dictyostele, while in the large species, P. cethiopicuin, 
medullary strands are formed as well as the external ring of 
meristeles. It may be noticed, however, that in P. alcicorne, the 
small bundle is actually an accessory medullary strand and may so 
far he held as some indication of the more complex state in 
P. cethiopicuin. In all the species examined, the leaf-trace takes its 
origin from more than one strand and the leaf-gap is closed by a 
long commissure. In P. cethiopicuin, it is established that the 
8 
14 15 16 17 
18 19 
Fig. 5. Platycerium cethiopicuin. Series of transverse sections of the 
rhizome of a young plant: 1 and 2 show formation of the dictyostele ; 12-14 
show first temporary accessory bundle (b) ; 16-24 show formation of the leaf- 
trace of the first leaf ; 25-34 show formation of leaf-trace of second leaf a, 
rootlets with a ring of sclerenchyma ; c, base of petiole of the first leaf. 
