C. H. Ostenfeld: Contributions to West Australian Botany. I. 



37 



They were very long; their apex was rounded, not truncate, and 

 they had a much stronger and thicker consistency than the typical 

 ones. I could not find any shoot of this peculiar sea-grass, only 

 the long leaf-blades the bases of which showed that they were 

 thrown off from the sheaths. Two intact leaf-blades were 80 and 

 105 cm long (thus exceeding P. australis, the longest leaf-blade 

 of which was 65 cm). The breadth of the leaves also differs: 



P. australis P. sp. 



6 — 11 mm 3 — 5 mm 



(average of 10 leaves: 8.1) (average of 6 leaves: 4) 



In transverse section (Fig. 

 23) the aberrant leaves differed 

 in several respects from the lea- 

 ves of the typical P. australis. 

 The epidermal cells have much 

 thicker walls and they are elong- 

 ated perpendicularly to the sur- 

 face. The sclerenchyma-strands 

 are more numerous, and while 

 in the typical P. australis the 

 strands are practically restricted 

 to a subepidermal layer (besides 

 the few scattered in the septa), 

 in this case they are also com- 

 mon in the outer parts of the 

 mesophyll inside the subepider- 

 mal layer. Other interesting 

 points are that the lacunæ in 

 the mesophyll are much nar- 

 rower than in typical P. austr., 



and that the ordinary cells of the mesophyll are filled with large 

 starch grains. I have never before met with this rich occurrence 

 of starch in the mesophyll of any sea-grass. 



Apart from these differences, the structure of the leaf points 

 to Posidonia, and the question is, strictly speaking, whether the 

 aberrant leaves belong to some modification of P. australis, or 

 represent a new hitherto unknown species of the genus. The 

 insufficient material at hand does not justify any definite decision 

 at present. I have mentioned it here only to draw the attention 

 of some later observer to this problem which seems worth solving. 



Fig. 23. Posidonia sp., fromCarnarvon. 

 Transverse section of a leaf-blade. 

 For explanation see fig. 18, with which 

 it is comparable. (About 150 /inat. size.) 



