1914] SNOW— DIAPHRAGMS OF WATER PLANTS 497 



stems 



rhizomes. Only three instances of the presence of perforated 



ragms 



UN 



nington 5), Hydrocharis morsus-ranae (Sauvageau 23), and 

 Limnobium Boscii (Montesanto 22). It is possible, however, 

 that the partitions noted in the roots of Eriocaulon and a few 

 species of Paepalanthus by Hackel (ii<;) may prove to be true 

 diaphragms. Only one reference (Duval-Jouve 7) has been made 

 to the presence of diaphragms in rhizomes. 



C. UNDER VARYING CONDITIONS OF SOIL MOISTURE 



Leitgeb (18) states that diaphragms are found "especially in 

 leaves of swamp and water plants." Duval-Jouve (10), in his 

 study of partly submerged grasses, found air spaces and dia- 

 phragms present in the immersed parts only. Solereder (32), 

 on the other hand, reports their presence in the aerial as well as the 

 submerged parts of the leaves of Stratiotes. Duval-Jouve (9) 

 found no diaphragms in the leaves of Iris germanica growing in a 

 dry habitat, but found them in /. pseudacorus and /. foetidissima 

 growing in water or wet places. He did not, however, test the 

 same species in the two habitats. 



* My work upon Scirpus validus has shown no apparent differ- 

 ence, as to the presence or structure of diaphragms, between the 

 immersed and the aerial parts. Experiments are at present in 

 progress to test the possibility of growing this species in drained 

 soil, and to investigate any structural changes which may take 

 place under drier conditions. 



IV. Structure 



A. OF DIAPHRAGMS 



In accordance with the reports for various plants, the dia- 

 phragms of Scirpus validus are one to several layers thick. 

 Commonly in old stems the greater extent of the diaphragm is com- 

 posed of one layer of cells, which increases to several layers around 

 the cross-bundle (fig. 7). As a rule, a diaphragm extends over one 

 air space, but Duval-Jouve (9) states that those of Cypcrus 

 Papyrus, Thalia dealbata, Butomus umbellatus, and Sagittaria 



