The Morphology of Ruppia Maritima. 87 
1. The general leaf arrangement is distichous (Pl. I, fig. 2; Pl. I, 
fig. 6), as in other members of the Potamogetonaceae so far as 
known, with the exception of Potamogeton natans and Potamogeton 
lucens, where a several ranked arrangement sometimes occurs 
(Irmisch, 1858 and Ascherson, 1889). 
2. A single plane, therefore, will intersect all points of leaf in- 
sertion on any stem (PI. I, fig. 1; Pl. VI, fig. 25). 
3. Moreover, on all branches, this plane of leaf insertion coincides 
with that of the main stem, a feature which combines with the 
methods of branching to produce the characteristic flat, fan- or sickle- 
shaped plants, a condition already noted in the Potamogetonaceae 
by Ascherson (1889) (Pl. I, fig. 2; Pl. I, fig. 6). 
4. The first, or basal leaf of every branch, which is in all cases 
a scale leaf, originates on that portion of the branch opposite to 
the subtending leaf—i. e., with its back toward the main axis of 
the shoot (Pl. Il, fig. 6, vs/). No internode is placed between it 
and the subtending leaf, so that it is therefore exactly opposite the 
latter.1 
5. The second leaf of every branch, in all cases a foliage leaf, 
is developed on the side of the branch adjacent to the subtending 
leaf, and thereafter ordinary foliage leaves of the branch proceed 
in regular distichous order (PI. II, fig. 6, 4, £(, &c.). 
In an account of the leaf of Ruppia I shall describe the three 
sorts of leaves, beginning with the ordinary foliage leaves, taking 
up next the subfloral leaves, and concluding with the scale leaves. 
C. Ordinary Foliage Leaves 
General Characters. The ordinary foliage leaves are ‘“ribbon- 
shaped”; long (7—17 cm.), and very narrow, (about 1 mm.) (PI. I, 
fig. 2; Pl. I, fig. 6). Although to the naked eye the margins appear 
entire, the microscope reveals at the apex a large number of one- 
to three-celled teeth, and these, with increasing distances between 
them, extend a considerable distance down the margins of the leaf 
(Pl. VI, fig. 26; Text-fig. 11). Upward from the base of the leaf, on 
each side, extending for 13-27 mm. are thin translucent appendages, 


' Goebel (1898, pp. 68—69) says, however, in speaking of the phyllotaxy of 
axillary branches in general, that, due to mechanical causes in the bud, 
“die bei weitem hiufigste Stellung der beiden ersten Blitter des Axillar- 
triebs eine /aterale ist, und erst die folgenden Blitter median oder mehr 
oder weniger schief gestellt sind.” 
