Box.— Vol. I.] CAMPBELL— MAIAS AND ZANNICHELLIA. n 



similar to, but simpler than that of the stem. In N. jicxilis, 

 except in the middle, the leaf is composed of but two layers 

 of cells. The center is traversed by a vascular bundle, 

 much like that of the stem, but without a definite endoder- 

 mis. In the younger stages, a single Hne of tracheids can 

 be seen penetrating into the base of the leaf, but no trace 

 of these is visible in sections of the fully developed leaf. 

 The bundle is surrounded by a layer of large cells, which 

 abut immediately upon the small intercellular space on either 

 side of the bundle. Naias maj'o?' (Magnus, 1870, p. 49) 

 differs markedly from all the other species in having a wel[ 

 marked epidermis consisting of small cells. This is correlated 

 with the thicker cortex of the stem^ Between the base of 

 each leaf and the stem are two scale-like structures, the 

 *' squamulas intravaginales," structures found very generally 

 throughout the Naiadaceas and Potamogetonaceas. 



III. The Roots. 



The primary root of the Naias Jiexllis is remarkable for 

 the absence of a root-cap, a fact which has apparently been 

 hitherto overlooked. Unfortunately my material of the 

 mature plants did not include the roots, and I am unable to 

 say whether this condition is also found in the later roots, 

 nor have I been able to find any reference to the subject 

 elsewhere. As to the position of the roots in the fully 

 developed plant, the writer cannot speak from his own 

 observations, and the account given by Magnus (1870, 

 p. 16) is not entirely clear. To judge from his fig- 

 ures, however, it would appear that the roots are pro- 

 duced in regular succession, one to each of the lower 

 nodes of the stem, arising between the two leaves of the 

 node on the side toward the leaf at the base of the 

 branch. 



»For further details of the structure of the leaves, the reader is referred to Magnus' 

 monograph. 



