Box.— Vol. I.] CAMPBELL—NAIAS AND ZANNICHELLIA. 



39 



apex, on examining the neighboring sections of the series 

 from which the figure was drawn, is seen to be one of two, 

 lying side by side and apparently resulting from a true 

 dichotomy of the stem-apex. A somewhat older stage is 

 shown in fig. 85, cut nearly at right angles to this view. At 

 first it is impossible to say which of these is to continue the 

 growth of the stem and which is the young inflorescence; 

 but this is soon determined by the rapid broadening of the 

 floral rudiment. 



A cross-section of the staminal primordium shows it to be 

 very early much extended laterally (fig. 84), and it soon 

 divides into two equal parts, one developing into the stamen, 

 the other into the lateral branch, in precisely the same way 

 as in Naias. The structure of the stem and arrangement of 

 the vascular bundles is much like Naias, but those of the latter 

 are better developed, especially as to the tracheary tissue, 

 which is conspicuous in the younger parts of the bundles, 

 but as in Naias becomes mostly destroyed by the subsequent 

 lengthening of the internodes. A single strand passes from 

 the single axial bundle of the stem into the lateral append- 

 ages, leaver, flowers, and lateral branches. The structure 

 of the bundle is concentric throughout. In the stem the 

 central strand of tracheary tissue is finally replaced by a 

 large canal (fig. 125). The rest of the bundle is made up 

 of thin-walled conducting tissue, and the whole shows a 

 well marked endodermis. The air-spaces are more numer- 

 ous than in Naias jlexilis and not quite so symmetrically 

 arranged. 



The leaves show two rows of large intercellular spaces 



on either side of the mid-rib, and these spaces are separated 



from each other by diaphragms at pretty regular intervals. 



The whole structure of the stem and leaf is very similar to 



that of other submerged aquatics. The sheaths below the 



nodes are usually not symmetrical, one side being higher 



than the other (fig. 81, 5/^), and are usually regarded as 



leaves destitute of a proper lamina. They are of very 



delicate membranaceous texture and composed of two layers 



of cells. They show no trace of a vascular bundle or 



mesophyll. 



( 4 ) J""« 3. 1897- 



