174 



BOTANICAL GAZETTE [September 



PHYLLOSPADIX 



Zostera 



qiiately studied, though Dudley (8; 9) gives a good general account, 

 and corrects several mistakes of earlier writers^ e, g., the supposedly 

 tuberous habit of the base of the stem as erroneously figured in Eng- 

 LER and Prantl (ii). Through the kindness of :SIr. C. P. Smith, 

 I have been able to study alcoholic material of P, Scoiderl from 

 Carmel Bay, California. As Dudley points out, the basal part of 

 the stem, far from being tuberous, is an elongated rhizome, along which 

 the leaves are arranged alternately right and left. In general plan, 

 the structure of the stem resembles that of Zostera marina, showing a 

 comparatively small central cylinder and two slender cortical bundles. 

 To the latter the lateral leaf trace bundles are attached, while the 

 median trace joins the central cylinder directly. These statements 

 apply equally to the ascending stem, represented in fig. 30, which 

 shows certain features more clearly on account of the absence of roots. 

 As may be seen in the figure, two lateral traces enter the stem on each 

 side of the median trace, and attach themselves to one of the cortical 

 strands which then sends in a branch to the central cylinder. Thus 

 the disposal of the leaf traces differs no more from that in Zostera 

 marina than does this from other species of Zostera. The central 

 cylinder is in most respects similar to that of Zostera, showing four 

 bundles in a section through an internode of the ascending stem. 

 In the upper part of such a stem the bundle derived from the median 

 trace of a leaf runs somewhat apart from the other bundles of the 

 central cylinder, and in general the vascular strands of this genus 

 show a tendency to be more widely separated than in Zostera. The 

 floral axis does not show the ring of bundles seen in Potamogeton, but 

 these are arranged in a tubular stele, and there are two cortical strands 

 as in the lower part of the stem. These features of the floral 

 axis are in accord with its specialized character in this species. 

 Numerous mechanical strands enter the stem from the leaves, espe- 

 cially in the ascending part of the stem, but they are not numerous nor 

 thick walled in the creeping stem. As in Zostera the pollen is fila- 

 mentous. The anatomical characters afford no reason for question- 

 ing the conclusion of Dudley, that the genus is derived from 

 Zostera, 



