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1904] CHRYSLER—CENTRAL CYLINDER 167 
upward course; toward the upper part of the tuber these enlarge and 
each is seen to be provided with an endodermis whose cells show a 
cutinized band girdling the radial walls. The strands now unite 
laterally into a flattened arch whose hollow is turned toward the 
cotyledon; by continued increase in the vascular tissue the arch 
becomes more and more nearly a complete circle. In fig. rz the 
cotyledon lies to the right; the individual sheaths have fused to form 
a common endodermis which is continuous outside and inside the 
arch; r is the trace of a root, which as usual leaves no gap in the 
central cylinder. Fig. r2 shows the central cylinder at a slightly 
higher level; the opening to the right faces the cotyledon, and is 
undoubtedly the cotyledonary gap. Soon this closes entirely, and at 
this level the vascular tissue of the stele becomes partly broken up 
into separate strands, some of which turn into the medulla; each 
strand and segment of the stele possesses its own endodermis. Amphi- 
vasal bundles are found at this level and in the later formed regions 
of the stem, but they are not so characteristic of Peltandra as of 
Symplocarpus, to which plant Peltandra evidently possesses many 
resemblances with respect to its central cylinder. The medullary 
strands are connected with the traces of all leaves above the cotyledon, 
and each trace leaves the central cylinder through a gap, around the 
edges of which the external and internal endodermis are continuous. 
Eventually, however, the endodermis becomes obsolete, and an increase 
in the number of medullary strands gives the stele the appearance 
characteristic of monocotyledons generally. It should be mentioned 
that the ring of bundles is not always present in the lower part of the 
tuber; in such cases bundles are so poorly developed in this region 
that a central cylinder cannot be said to exist below the cotyledonary 
gap. 
AZANTEDESCHIA AETHIOPICA (the ordinary calla lily) and Z. ALBo- 
MACULATA may be described together, since the seedlings are very 
similar. As the stele of the root merges into that of the hypocotyl 
it assumes a pith into which several strands turn from the original 
vascular ring, and soon the whole stele is converted into a network 
of anastomosing strands. From this network about six bundles are 
Siven off to the cotyledon, whose base forms a sheath around the 
younger leaves. In the succeeding regions of the stem the bundles 
