232 , MK. H. N. EIDLET ON THE 



DESCRIPTION OF THE PLATES. 



Plate XL 

 Nephrodium (§ Sagenia) sienojpJiyllnm, Baker, n. sp.—Fig. L Frond. Fig. 2. 

 Enlarged portion, showing sori. 



Plate XIL 



Trichomanes Hosei, Baker, n. sp.— Fig. L Frond. Fig. 2. Enlargement of 

 thecse. 



cxirrin 



On the Freshwater Hydrocharidjese of Africa and its Islands. 



By H. N. EiDLfei M.A., E.L.S. 



[Eead 1st April, 1886.] 



(Plates XIIL & XIV.) 



Of the eleven genera of Hydroeliarideffi Inhabiting fresh water, 

 seven occur in Africa and the adjacent archipelago. The section 

 Hydrilleae is represented by the genus Hydrilla and Lagarosiphon. 

 The former genus consists of a single polymorphic species, very 

 \ridely distributed and common throughout Tropical Asia, and 



g also in Australasia; it is found in Africa, but is 

 apparently not so abundant. Lagarosijilwn is a genus very cha- 

 racteristic of Africa, all the species known being natives of that 

 region or of Madagascar, with the single exception of L. Box- 

 hurghii, an Indian plant of very different habit, wliich has, how- 

 ever, been found in Socotra, but there it is possibly an intro- 

 duction. The species are all very closely allied, and not easy 

 to study from dry specimens, as the flowers are exceedingly deli- 

 cate and the male flowers are comparatively rarely met with. One 

 of the chief distinctions between Sydrilla and Lagarosiphm is 

 that the leaves in the former are in whorls, in the latter scattered ; 

 in some species of Lagarosiphon, however, there is a great ten- 

 dency for the leaves to become opposite, especially towards the 

 apex of the stems. "" • • - - 



In the ' Genera Plantarum ' it ' is stated that there are no 



in L. rubella 



stamiiiodia in the female flower; this is usually the case, but 

 they do occur in at least one species in the form of slender short 

 filaments. 



two 



occur within the area. One, Vallisneria, comprises a single 

 species widely spread over the whole world. Blyxa contains the 

 common Indian plant, B. BoxhurqUi, Eich.. which is found also 



