106 



J. O. HAGSTRÖM, 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. obiusifolius, about a leaf-\vidth's distance from it, or 

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

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



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

 is visible ontwardly 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. obtusifolius 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. denticulaius 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. pusiUus L. ! 



P. exignns n. sp. — Fig. 42. 



Caulis humilis ad basin solum ramosus tenuis filiformis 

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

 aria, latitudinem maximam infra medium pra?stantia, basi at- 

 tenuata, obtusa, caulina inconspicue mucronulata, ramulorum 

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

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

 '"'»• lh(; (5 mm), caducae, biglandulosrc, subpaucinervia>. Palmiculiis bre- 



lacnnar Bysten: and the bud- * o j. 



epidermai stranda (*tr), ca. »f»; vis (sub anthcsiii 5 mm, dcfloratus 8—10(15) mm) teres. Spiea 



''■ Tranavei on of the . . , n _ ,. ... . .. _ «, v -. . , 



pednnole, showing ita form, brevis deiisa 2— 3-verticillata (4— ()-tlora). tiructus parvus, 1,g— 

 aispositi U on X2L 1." ™ longus, 1 mm latus, oblique obovatus, dorso rotuudatus 



bondiea, ,'; " ''- 1 ' 1 . ". (siccus subcarinatus), rostro apicali brevissimo. 



from i in- nde, 6, back-view, ,. " * 



Among the f©W spccimcns of this Bpecies I havc had at 

 hand a singlc onc has bcen found with a doveloped rhizomo and a shoot arising from 

 it. To judge from this the rhizome creeps snpcrficiallv in the bottom. Rhizomatic 

 winterbnds are probably not produced in accordancc with the condilion of fhings of 

 om indigenous pusillus-like Bpecies. toto Buofa organs, on the oontrary, tlu^ small 

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



Fig. 41. /'. antaicus Hao- 

 -ik. A, Dppei portion "i a 

 atem-leaf abowing the charac- 

 teriatic nervation, ', ; ; B, Trana- 

 1 1 1 te section ol the middle 

 part "1 a Btem-leaf, showing 



