

1907] CHRYSLER— POTAMOGETONACEAE 169 



leaves. In the creeping stem, however, the two opposite bundles are 

 seen from the foregoing to be connected with the origin of branches. 

 As in the leafy shoot, vessels are present only at the nodes, and are 

 represented by a cavity elsewhere. The endodermis is plain, of 

 U"form, and suberised. Fig. i6^ representing the creeping stem of P. 

 natans, which should be compared with fig. ij, shows another point 

 of difference between the creeping and the leafy stem. While cortical 

 bundles are abundant in the latter, they are much scarcer or absent 

 in the former^ owing apparently to poor development of leaves and the 

 absence of stipules. In case cortical bundles are absent in the leafy 

 shoot, they are lacking also in the creeping stem, as may be seen from 

 the figures of P. pulcher. In accordance with the sheathing char- 

 acter of the reduced leaves, the leaf traces enter the central cylinder 



j separately, as may be well seen in P. perjoliatus or P. heterophylluSy 



which have better developed basal leaves than has P. pulcher, 



f The floral axis. — Schenck (28) and others have not failed to 



notice that the peduncle has a different disposition of bundles from 

 that in the leafy shoot, but the earlier observers have apparently over- 

 looked the regularity in the arrangement of the bundles. Fig. 23 

 shows the appearance of a section through the fertile part of the floral 

 axis of P. natans. The arrangement is evidently circular, and the 

 bundles are collateral. Branches leading to the flowers do not have a 

 gap above their point of exit, but spring from one bundle or from two 

 adjoining bundles. Well-developed tracheary tissue is present in 

 all of the bundles, in marked contrast to the condition seen in an intcr- 

 node of the vegetative axis. Fig. 24 represents an appearance which 

 occasionally occurs; here the bundles constitute a nearly closed 

 vascular tube. The circular arrangement of bundles occurs in every 

 species which I have examined, even in such slender forms as P. 

 hyhridus, the peduncle of which shows four separate strands, each 

 surrounded by an endodermis {fig. 26). The basal part of the axis 

 shows the same arrangement as that represented in the figures, but 

 the strands are apt to be more widely separated. Cortical strands 

 are also present in the peduncle of species such as natans, which show 

 many such strands in the leafy stem {fig. 25) ; they cither join bundles 

 of the circle or dwindle away shortly after reaching the fertile part 

 of the axis. A ring of collateral bundles in the floral axis of Eleo- 



