313 



MAIDENIA : 



A New Genus of Hydrocharidace^. 

 By a. B. Rendle, D.Sc, F.R.S. 



(Plate 545.) 



The Director of the Sydney Botanic Garden has recently sent 

 me a few specimens of a small submerged water-plant collected in 

 1906 near the King River, East Kimberley district, North-West 

 Australia, by Mr. W. V. Fitzgerald, who recognized the plant as a 

 new genus, and whose name I have adopted. 



The specimens represent a delicate plant 2 to 2j inches high 

 with the habit of the African Lagarosiphoii. The slender erect 

 simple stem is attached at the base by a dense cluster of thread-like 

 roots. Its internal structure resembles that of other submerged 

 aquatic Monocotyledons of similar habit. The sharply delineated 

 central stele consists, as seen in transverse section, of densely 

 packed small-celled fibrous tissue surrounding a central air-space 

 and an irregular ring of somewhat smaller more peripheral air- 

 spaces. Round the outside of the stele are generally two layers 

 of parenchyma, and the rest of the section is occupied by the 

 cortex, consisting of a very open network of air-spaces separated 

 by single layers of parenchyma ; this extends to the epidermal 

 layer. Through the cortex a thin strand of the elongated fibrous 

 cells, surrounded by a definite one-layered sheath of parenchyma, 

 runs out to the base of each leaf, up t'.e centre of which it is 

 continued as a not very conspicuous midrib. 



The stem is covered from base to apex with numerous almost 

 thread-like leaves, one at each node, but with internodes almost 

 entirely suppressed. The leaf-base broadens somewhat to the 

 insertion, but there is no definite sheath and no stipular structure. 

 The leaf is flat and narrow-linear, tapering above to a point; 

 along the margin at intervals about equal to or exceeding the width 

 of the leaf are small upwardly pointing spine-cells which protrude 

 on a shallowly triangular base; the leaf-apex ends in one or a pair 

 of similar spines. The internal structure is very simple ; on either 

 side the narrow midrib are air-spaces beyond which the lamina is 

 only two cell-layers in thickness. The inflorescences are of a very 

 reduced type. In the male plant they are grouped at intervals on 

 the stem ; several (3-5) spathes in successive grades of develop- 

 ment arise in the axil of each of two leaves which are almost 

 opposite, forming together an apparent whorl of spathes — a kind 

 of verticillaster ; associated with each spathe is a minute hair-like 

 structure. The spathes in each leaf-axil probably represent a 

 unilateral cyme ; in addition to these the same leaf-axil shelters 

 a pair of opposite sheathing bracts of different ages, each of which 

 envelops a very young group of spathes. This arrangement, 

 which is made out with some difficulty from the very meagre 

 dried material, suggests a flowering period which is continuous so 

 long as the conditions are favourable or the life of the plant 



Journal of Botany. — Vol. 51. [November, 1916.] 



