REVUE BRYOLOGIQUE 75 



cells, the completeness of the peristome, and the shape of 

 the capsule have played the most important part. The 

 Le:sk€aceae are characterized chiefly by the structure and 

 arrangement of the leaf cells, the peristome playing an 

 important part in the arrangement of the genera ; the 

 Neckeraceae and allied genera, by the general habit, struc- 

 ture and arrangement of the leaf cells and the general 

 structure of the peristome ; the Ibjpnaccae by the general 

 habit, slructure of the leaves and the perfect peristome. 



"While these characters should certainly be considered 

 in any system there are others that should receive atten- 

 tion. The presence or absence of a central strand has been 

 httle considered, yet the central strand is the physiological 

 homologue of the vascular bundle that plays so important 

 a part m the general classification of plants' and though ot 

 much less importance will, I believe serve to indicate rela- 

 tio^nships otherwise obscure, there are cases of course 

 where the central strand is vestigial or wholly wanting. 

 I imagine that it would not be easy to demonstrate vascular 

 bundles in Wolfia although it sposition as a vascular 

 plant is unquestioned. The central strand is usually corre- 

 lated with the presence of a costa in the leaves. A vestige 

 of a strand is present in both Ufjpnum chrysophi/Ilum 

 and //. stellatum but the costa is usually lacking in stella- 

 tum and usually present in chrysophyllum. In Ihjpnvm 

 vcrnicosimi^ Dtjchelima and a few other aquatic or sub- 

 aquatic forms the costa is well developed and the central 

 strand lacking. Such cases are the exception and this 

 character must certahily be of as much value as the size 

 and shape of the capsule, yet if it were so treated Amblys- 

 teghnn^ Plagiotheciiim^ and some other genera would be 

 badly shaken up. 



Another important character wich has seemingly been 

 ignored is the presence of very fine parallel transverse 

 lines on the outer basal plates of the peristomal teeth. 

 A complete normal Ilypnaceous peristome consists of an 

 outer row of 16 teeth composed of a cell wall thickened in 

 several layers, and an inner row of the same number of 

 teeth much thinner and alternating with slender hair-Hke 

 processes called cilia. In Hypnuin, Amblystcgiwn, Bra- 

 chyUxvfm, Eurhynchmm^ ' Plagiothecium^ Cnmplothe- 

 ciitm, Orthothecium, isothrchuh, Thuidiiun and smaller 

 allied genera these lines are present on the basal segn^ents 

 of the teeth, extending nearly or quite half-way to the apex. 

 The upper portion of the teeth is usually papillose. Although 

 the number and length of the cilia, and the shape and 

 structure of the leaf cells may vary greatly, this character 

 si constant. The number ot the segments of the teeth 



