KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. N:0 5. 



257 



ish plant. — P. perfoliatus v. Jacksoni Lees, The bot. Record Club Report 1880, 

 p. 50, is a form of the hybrid P. Cooperi Fryer, see above, p. 62! 



Distribution: P. perfoliatus is common through the whole of the Scandi- 

 navian peninsula and spreads in the north to Lapponia murmanica (87, Kihlman, 

 hb. Stockholm.). In Asia it occurs, in the Yenisei-valley northward to the Nikan- 

 drovskii östro v, 70° 20' N. L. (f. longifolius Tis.). I ha ve seen it from Yenisei (hb. 

 Stockholm., Uppsal.) and also from Bering Island (79, Kjellman, hb. Uppsal.) and 

 it seems likely that the northern boimdary line coincides with that of P. natans and 

 gramineus, or the year-isotherm of about — - 5° C, with the usual Siberian curve in the 

 north of about 5 degrees. The same line we also meet with in N. America. 



From this northern line it spreads to North Africa and India. India orientalis, 

 herb. Wight (hb. Stockholm.), small-leaved, peduncles very short, 20 — 25 mm, fruit 

 with strongly convex sides. From there it has probably spread to Australia, where 

 it also occurs small-leaved in New S. Wales (97, J. H. Maiden, hb. Bot. Gardens, 

 Sydney). No specimens, however, are seen from North Australia. Nor have I seen 

 specimens from South America. 



P. perfoliatus L. x praelongns 



WULF. 



(P. cognatus Ascherson 

 et Graebner, Synopsis mit- 

 teleur. Flora 1897. 317). — 



Fig. 118. Fig. 118. A, P. perfoliatus L. Top of stem-leaf, f B, P. perfoliatus X 



xi- Vv x-f 1 pra-longus, Top. of stem-leaf, a little enlarged, showing the peculiar inter- 



1 Jiave Seen DeaUtllUI me diRte form of the apex. C, P. prcelotiffus Wulf. ca. f. 



specimens of this hybrid from 



Denmark, where it occurs in Varming Lake and in its outlet Nibså near Ribe (96 and 

 99, Baagöe, hb. Stockholm., Uppsal.). Leaves with cordate base and rounded apex 

 in a very interesting way intermediate between the two parent-species : The börder 

 is namely in the very top bent över as in P. prcelongus, though not so strongly, and, 

 besides, endowed with a faint canaliculate lip according to the shape of the apex of 

 P. perfoliatus. See fig. 118, B. Leaf-margin without hair-like teeth, in this respect 

 consequently corresponding to the hybrid P. undulatus as this commonly occurs. Li- 

 gules intermediate, somewhat shorter and more deciduous than those of P. praäongus. 



In the stem-anatomy we find an endodermis corresponding with that of P. 

 perfoliatus, while the bark, as in P. pradongus, is furnished with vascular and bast 

 bundles, but fewer in number by the influence of P. perfoliatus. 



The German £pree-specimens of this hybrid are said to have the leaf-margin 

 serrulate: Blätter am Rande von ziemlich entfernten feinen Zähnchen rauh. If 

 this be true we should have two varieties: one with serrulation, the other without it. 



The former might be named: 



a. denticulatus n. var. — Folia margine rare denticulata. 



The latter: [i. laevis n. var. — Folia margine integerrima. 



K. Sv. Vet. Akad. Handl. Band 55. N:o 5. 33 



