The Morphology of Ruppia Maritima. 79 



The course taken by the cortical bundles, although simple, is not 

 quite as evident. The cortical bundles are entirely independent of 

 the central bundle, never connecting with it, so far as I have been 

 able to ascertain. Their position can be best shown by the use of 

 figures selected from a series of cross sections. A cross section in 

 the region ot a node, just below the point where the leaf is given 

 off, is represented in PL V, fig. 19. Here the cortical bundles are 

 situated in the outer cortex, not quite diametrically opposite each 

 other. This figure also shows the axial bundle somewhat dilated 

 radially. PL V, fig. 20 shows the edges of the leaf sheaths appearing 

 at the cleft at the upper side of the figure. The cortical bundles 

 occupy about the same position as before, but the axial bundle is 

 commencing to give oif its two branches — to the leaf and axillary 

 branch. In PL V, fig. 21 the leaf sheaths are still more separated 

 from the stem; the two large leaf and branch bundles are now dis- 

 tinct from the axial stem bundle; the cortical bundles have moved 

 outward slightl}^ and a new cortical bundle appears nearer the 

 central bundle. Since the section is cut slightly obliquely, and the 

 right side represents a portion higher up in the stem, only one of 

 the pair of new cortical bundles thus appears. PL V, fig. 22 shows 

 both, however, and also represents the former pair of cortical bundles 

 as moving gradually into the still further separated leaf PL V, 

 fig. 23 shows the leaf with its lateral (cortical) bundles, separate 

 from the stem, and fig. 24 does the same for the branch which 

 it subtends. 



It is clear, therefore, that the cortical bundles of the stem furnish 

 the lateral nerves of the leaf. It will be seen also that not only 

 do the cortical bundles have no connection with the axial bundle, 

 but also that a new pair arises at each node to pass into the leaf 

 at the node next higher up. After a careful examination, I find 

 absolutely no connection betvN^een these successive pairs of cortical 

 bundles. 



Although the figures and description of De Bary (1884, p. 274) 

 for Potamogeton crispus seemed to present an arrangement similar 

 to the above, the work of Chrysler (1907), which appeared while 

 this paper was being prepared for publication, corrects De Bary's 

 account but confirms my investigation of Ruppia maritima. Chrysler's 

 conclusion (1. c. p. 171) is undoubtedly correct that " this condition 

 has in all probability been derived by reduction from that in which 

 the cortical bundles joined the central cylinder at the next node 

 below the insertion of the leaf to which they belong." 



The cortical bundles of Zoster a marina (De Bary, 1884, p. 275 ; 



