106 



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



by often s-formed cross-veins. Finally they join the midrib at a greater distance 

 from the very apex than in P. ohtusifolius, about a leaf-width's distance from it, or 

 often a little more. Cf. figs. 41, ^, 51, B. In this respect the species resembles more 

 P. pusillus. The middle vascular bundle is surrounded by a group of small lacunae 



and a row of large channels which, by suitable enlargement, 

 is visible outwardly like a light stripe along the midrib. The 

 mechanical system within the lacunar area may best be seen 

 in the adjoined figure. 



The front-field of the stipular sheath is 8— 9-fibrous, where- 

 as P. ohtusifolius is 14-fibrous, and besides has open ligules. 

 The stem-structure is recognized by the fact, that it is 

 endowed with a pseudo-hypoderma along the endodermis beside 

 the usual subepidermal strands. The crosscut-form of the cen- 

 tral cylinder is roundish or oval and the bundles are arranged 

 according to the circular or oblong (in stouter stems) diagram. 

 Though the fruit-form is unknown this species can easily 

 be identified by the characters given above. Our species can- 

 not be identic with P. denticulatus Link, since that species, 

 for the rest little known, has acute leaves. 



Distribution. Africa, S:t Antao, Cape Verde Islands. 

 Leg. Lowe (hb. Stockholm.). Cfr Thiselton — Dyer, Flora 

 of trop. Africa, VIII, 2, 1901, 222, under P. pusillus L. ! 



exigims n. 



sp. — Fig. 42. 



Caulis humilis ad basin solum ramosus tenuis filiforniis 

 teres vel subteres, internodiis brevibus, 10 — 20 mm. Folia line- 

 aria, latitudinem maximam infra medium prsestantia, basi at- 

 tenuata, obtusa, caulina inconspicue mucronulata, ramulorum 

 mucronata, trinervia, nervo medio reticulata, 20—35 mm longa, 

 1 — 2 mm lata (folia floralia 15 — 20 mm longa). Ligulce breves 

 (5 mm), caducse, biglandulosse, subpaucinervise. Pedunculus bre- 

 vis (sub anthesin 5 mm, defloratus 8—10(15) mm) teres. Spica 

 brevis densa 2— 3-verticillata (4— 6-flora). Fructus parvus, 1,5— 

 1,75 mm longus, 1 mm latus, oblique obovatus, dorso rotundatus 

 (siccus subcarinatus), rostro apicali brevissimo. 



Among the few specimens of this species I have had at 

 hand a single one has been found with a developed rhizome and a shoot arising from 

 it. To judge from this the rhizome creeps superficially in the bottom. Ehizomatic 

 winterbuds are probably not produced in accordance with the condition of things of 

 our indigenous pusillus-like species. Into such organs, on the contrary, the small 

 undeveloped branches, present on the lower portion of the stem, are transformed. 



Fig. 41, P. antaictts Hag- 

 STK. A, Upper portion of a 

 stem-leaf showing the charac- 

 teristic nervation, ^ ; JJ, Trans- 

 verse section of the middle 

 part of a stem-leaf, showing 

 the vascular bnndle {»i), the 

 lacunar system and the sub- 

 epidermal strands [sir), ca. ' Jo. 

 C, Transverse section of the 

 peduncle, showing its foi-m, 

 the lacunar system, and the 

 disposition of the vascular and 

 bast bundles, "j"; i>, Pistil, o, 

 from the side, b, back-view, f. 



