88 A. H. Graves, 
which I have termed the stipular sheaths (Pl. I, fig. 2; Pl. I], 
fig. 6). In external appearance the leaves very closely resemble 
those of Potamogeton filiformis and Potamogeton pectinatus, both 
also typical submerged plants (Morong, 1893). The leaves of 
Zannichellia and Althenia are also macroscopically very similar: 
those of all species of Naias are much shorter with strongly serrate 
or toothed margins.1 
Development of the Folage Leaf. Different stages of leaf 
development are represented in Pl. I, fig. 1; Pl. VI, fig. 25, lon- 
gitudinal sections of a vegetative bud, where the youngest leaf 
is the protuberance at one side of the growing point (LV//! 
in Pl. I, fig: 1).. The next older leaf primordium, shownjen 
the right of the growing point (PI. I, fig. 1, Z/7), has already 
l slightly elongated, until now it extends 
f beyond the growing point. Successively 
older stages are represented by LY, 
= we IOV, LAV, OIC: 
J G al Pl. VU, fig. 43 represents a transverse 
3 y ~ section through a similar bud cut through 
about the region of the line @é in Pl. I, 
{ fig. 1. Therefore, we find here the different 
members in exactly the same orientation 
| 4 as in PI. I, fig. 1. Thus, the outermost leaf, 
Z (| L/, embraces with its sheaths all the 
| y internal complex, just as is shown by L/ 
s 
{] with its sheaths in PI. I, fig. 1. The next 
) inner member is 4!/), or the lowest and 
a largest foliage leaf of the axillary bud of 
Figure 11.—The marginal 7 7 ; then a section through the apical 
leaf teeth, showing variation : ‘ 
in cell arrangement. >< 300, Portion of the scale leaf which envelops 
; this axillary bud; next the leaf sheaths of 
the next upper main leaf, L//, appear, which brings us to a cross 
section of the central stem: without going into more detail it is 
sufficient to note that the remaining parts may be correlated to their 
corresponding longitudinal sections in the same way. ~The line a6 

1 All these species belong to Hansgirg’s (1903) “ Vallisneria-Typus 
der Strémungsblitter,” a physiological group showing little differentiation 
into blade and petiole and characterized by the lack of cuticle, hair 
structures and stomata, by the absence of any considerable amount of 
supporting tissue, and by the ribbon-like, isolateral form. 
