28 



J. O, HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



apice ssepe recurvata, caulina omnia sequilata, 50 X 0,8 — 1 mm, vaginis 15 mm (summis 

 8 mm) longis, ramea angustiora (0,75 mm), superne paulo longiora, vaginis 20 mm 

 longis. Vagince badeo-marginatse juniores integrse ligulis membranaceis 5 — 8 mm 

 longis. Pedunculus brevis (sub anthesi); spica florens brevis (10 mm) 8-flora, floribus 

 minoribus. Pollen ovale magnitudine media. Stylus brevis, stigmate humili, postice 

 in rostrum breve protracto; fructus non visus. — Fig. 8. 



Anatomy of the stem : Epidermis-cells elongated and rather wide, almost of the 

 same width as the bark-cells supporting it (hypoderma). Endodermis-cells almost 

 insensibly thickened (faint ^i-cells). The strands of the cortex and the central cylinder 

 as in P. jilijormis, from which the anatomy but little differs. The leaf-anatomy 

 also corresponds nearly to that species. Consequently there are two rows of larger 

 b 



Fig. 8. P. rostratiis Hagstk. A, Apex of a stem-leaf, 'y^ ; B Apex of a branch-leaf, Y", the cross-lines represent the bottoms 

 of the iacunffi, a, h, See C .' C, Transverse-section of a leaf (middle part); a, hj vascular bundles (nerves), ^/; D, Pietil from 



the side, 



E, Stigma (more enlarged) seen from above. 



lacunae on each side of the small lacunae round the mid-bundle. Seldom someone 

 or other of these greater lacunae is longitudinally divided into two (fig. 8, C, to the 

 right!). Towards the leaf-apex the channel-bottoms are scarcely visible outside. The 

 marginal nerves run subepidermally only a couple of cell-layers from the epidermis, 

 and join the mid-bundle quite in the utmost tip (fig. 8, A, B). 



This description is made after a single little flowering specimen and, of course, 

 the statement of the length of the peduncle, spike and of the whole plant wants to 

 be completed by further researches. Nevertheless it is even without fruit easily re- 

 cognizable from the slightly recurved leaf-apex, that in its form much reminds of 

 P. peciinatus, and from the stigma protracted backwards in a little beak as in P. 

 recurvatus m., thus combining in an interesting way different groups of the subgenus 

 Coleogeton. The connate sheaths, the ramification and other characters yet show its 

 close relation to P. filiformis, the group of which it completes by the acute leaves, 

 whereas the other species have obtuse leaves. 



Distribution, Asia. Mongolia bor. Desertum a Thian Schan boream versus, 

 1877, PoTANiN (hb. Stockholm.). 



