OP ARTS AND SCIENCES. 65 



which have a frond of loose structure, the procarp is borne at the 

 apex of a short branch, which does not differ in any marked way from 

 the other branches. In some of the denser species, however, this 

 branch is somewhat modified. This is particularly striking m B. den- 

 sum, Sirdt. (cf. Sirodot, Les Batrachospermes, Plate XIII. Figs. 6, 9, 

 and 10), wlure the procarpic branch much resembles some of the 

 simpler ones found in Tuomeya. This special branch in B. densum is 

 by no means modified to the extent that the majority found in Tuomeya 

 are. In Lemanea the procarpic branch is very different from any 

 found in Batrachospermum, and seems more complicated in some ways 

 than in Tuomeya. The procarpic branch iu Lemanea arises from a 

 cell placed against one of the lateral tubes. It is usually tliree or 

 four cells long, and bears at the tip an elongated trichogyne which 

 projects externally. The lower cells of this branch, in some species, 

 (cf Ketel, Anatomische Untersuchungen iiber die Gattung Lemanea, 

 Inaug. Diss., Berlin, 1887,) produce a number of short brauchlets 

 similar to those in Tuomeya. 



The trichogyne of Tuomeya is almost exactly like that of Batra- 

 chospermum, and yet in some of its various shapes it much resembles 

 the trichogyne of certain of the simpler species of Lemanea. It is 

 not, however, modified to any such extent as are the trichogynes of 

 the ordinary Lemanece. The first stages in the formation of the 

 cystocarp are also essentially like those of the cystocarp of Batracho- 

 spermum. Therefore, we may say that in the position and structure 

 of the female organs, as well as in the development of the cystocarp, 

 Tuomeya approaches certain of the more complex species of Batra- 

 chospermum on the one hand, and certam of the simpler forms of 

 Lemanea on the other, thus occupying, in regard to these structures, 

 an intermediate position between these two genera. 



Harvey considered' that a solid filamentous axis, coated externally 

 with moniliform filaments, was characteristic of Batrachospermum, 

 while Lemanea possessed a cylindrical and hollow frond, whose walls 

 were laxly constructed within. Tuomeya seemed to him to possess 

 the solid axis of a Batrachospermum, shut up within the tube of a 

 Lemanea, and coated externally with the filaments of a Thorea. Har- 

 vey's idea of the relationship is a very good one. The solid axis, 

 to be sure, more nearly resembles that of certain species of Lemanea, 

 but in its earlier stages is almost exactly like that of Batrachospermum. 

 The frond at one period is a hollow cylinder enclosing this axis, but it 

 has developed like that of a true Batrachospermum. In its extreme 



VOL. XXV. (N. S. XVII.) 6 



