The Morphology of Ruppia Maritima. 87 



1. The general leaf arrangement is distichous (PL I, fig. 2; PL II, 

 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 (PL I, fig. J ; 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 II, 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 II, fig. 6, vsl). 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 ordei- (PL 11, fig. 6, /i(^), l^^^), Sic). 



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.) (PL I, 

 fig. 2 ; PL II, 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, 



' Groebel (1898, pp. 68 — 69) says, ho^wever, in speaking of tliephyllotaxy of 

 axillary branches in general, that, due to mechanical causes in the bud, 

 " die bei weitem haufigste Stellung der beiden ersten Blatter des Axillar- 

 triebs eine laterale ist, und erst die folgenden Blatter median oder mehr 

 oder Tveniger schief gestellt sind." 



