KUNGL. SV. VET. AKADEMIENS HANDLINGAE. BAND 55. N:0 5. 127 



leaves, the turios and the stem anatomy plainly bear witness of P. Vaseyi. P. diver- 

 sifolius is quite out of question for the sake of its characteristic peduncles and fructi- 

 fication, of which nothing at all can be traced in the P. lateralis, even by the mi- 

 nutest observation. 



As the other parent, that must have only submerged leaves one could think 

 of P. foliosus, or panormiianus, or picsillus. With respect to the first-mentioned, it 

 has sharply keeled fruits as P. Vaseyi, whereas the hybrid often, easily gets a weaker 

 keel and the basal part of the lid like that of P. pusillus. To this may be added, 

 that neither the spike nor the peduncle is influenced by P. foliosus, that has very 

 short peduncles and few-flowered spikes. As to the turios, generally consisting of 

 transformed tops of branches, they evidently deviate toward fusiUus rather than to 

 P. panormitanMs. All this taken into consideration the choice between those three 

 cannot be difficult. All deviations from P. Vaseyi, even the leaf-structure, aim at 

 P. pusillus. 



The hybrid is not met with out of the distribution-area of P. Vaseyi and seems 

 to occur in waters where P. Vaseyi and pusillus are growing together. It is known 

 in three different forms: 



1. Endowed with floating leaves, usually however narrower than in P. Vaseyi 

 (influence from P. pusillus); always barren. It could conveniently be named: 



f. iucompletus n. f. — Sterilis; foliis summis vere natantibus. 



2. Another form without floating leaves, i. e. more pusillus-Wke in habit, but 

 with leaves as to structure more like the submersed leaves of P. Vaseyi. For this 

 form I propose the name: 



f. subcompletus n. f. — Forma ssepe fructibus paucis evolutis, foliis submersis. 



3. The third form resembles P. pusillus v. temiissimus in such a degree that 

 Rev. MoKONG has taken it for this plant. It has, however, more sharply pointed 

 leaves and slender buds approaching in form to P. Vaseyi. Yet I desist from naming 

 it, until more material can be had and further observations eventually made. It 

 grows together with the suggested parents in the lake Quinsigamond near Worcester, 

 Mass., U. S. A., where it was collected by Pvcv. Dr. Th. Morong. 



Distribution. N. America, In flumine Charles, Dedham, Mass., U. S. A., 

 80, Morong (hb. Stockholm, et Uppsal.) According to Robinson and Fernald, Hand- 

 book flower, pi. 1908, 76, it is met with as well in Connecticut and westward to 

 Michigan. 



P. groeiilaiidiciis n. sp. 



Caulis conipressus (1,8 : 1), simplex vel subramosus, internodiis 3 — 4 cm longis 

 vel ultra. Folia uniformia, ca. 60 X 1 mm, angustissime linearia, 5 — 9-nervia, apice 

 triangularia v. subcuspidata v. rotundata cum mucrone verrucfeformi (vide fig. 55, 

 A, a, b, c/), basi ad nervum medium ± lacunosa, nervis minutissimis. Ligulse fissse. 



