1895.] Preliminary Statement on the Sorus of Dansea. 141 



an interesting intermediate position ; the replacement of the sunken 

 sporangia of Ophioglossum by projecting sporangiophores in Helmin- 

 thostackys suggests, as already indicated in the preliminary statement 

 ('Roy. Soc. Proc.,' vol. 50, p. 265), an interesting analogy with the 

 hypothetical origin of the strobilus of JEquisetum from a body of the 

 nature of a sporogonial head. 



The chief object in view in these investigations has not been the 

 mere tracing of homologies of parts among living forms ; but, by 

 developmental study and comparison, the following out of the prob- 

 able methods of progression in the evolution of the more complex 

 from the simpler types. It is believed that all the three methods of 

 increase in number of separate sporangia, suggested in the former 

 memoir (' Phil. Trans.,' 1894, vol. B, p. 473), have been employed, 

 viz. (i) septation, (ii) branching or chorisis, (iii) a reversion of vege- 

 tative parts to the sporogenous condition. In addition to these, 

 however, there has probably occurred also an eruption of appendicular 

 organs from a previously smooth surface. This has already been 

 suggested elsewhere ('Annals of Botany,' vol. 8, p. 343) ; the 

 sporangiophores of Helminthostachys may be taken as an interesting 

 example of such eruption. It will be thus seen that the memoir, of 

 which this is a very brief abstract, touches some of the most funda- 

 mental conceptions of the morphology of vascular plants, approaching 

 them, not from the point of view derived from comparison of higher 

 forms, but from the study and comparison of organisms which are 

 believed to be nearer to the border line between Bryophyta and 

 Vascular plants, viz., the Homosporous Pteridophyta. 



II. " Preliminary Statement on the Sorus of Danma." By 

 F. 0. Bower, F.R.S., Regius Professor of Botany, Univer- 

 sity of Glasgow. Received November 29, 1895. 



The sorus of Dancea, though its structure in the mature state has 

 been repeatedly described, has not yet been studied as regards its 

 development. 



The oblong, cake -like sori lie parallel to one another on the lower 

 surface of the leaf, their longer axes following the course of the 

 vascular bundles. Each sorus consists of two rows of loculi, of 

 approximately equal size, completely sunk in the rather massive 

 tissue of the wall. Dehiscence is described as being by a pore at the 

 apex of each loculus. 



The sporogenous tissue of each loculus is usually referable to the 

 segmentation of a single superficial cell, which gives rise to it, 

 and to the portion of the sporangial wall above it. There is, how- 

 ever, great variety of bulk, number of cells, and mode of segmentation 



