142 Preliminary Statement on the Sorus o/Danaea. [Dec. 5, 



in adjoining sporangia; though the sporangia of the same sorus 

 develop simultaneously, such extreme differences of number as 

 between 4 and 16 cells may be seen in the same section. More- 

 over, the whole sporogenous group is not always referable to a 

 single parent cell. These facts stand in marked contrast to the 

 uniformity of size and segmentation so characteristic of the Lepto- 

 sporangiate Ferns. 



The dehiscence is by slits, which appear in the sporangial wall 

 above the loculus. By the drying and contraction of the adjoining 

 cells the slit gapes widely, and appears as a pore ; but the details 

 are very like those of other Marattiacese, excepting that there is no 

 M annulus " of indurated cells. This, which is absent in Dancea, 

 where the loculi are deeply sunk, is present in those Marattiacea? 

 in which the sporangia project as separate papillae. In the latter 

 case the annulus is mechanically effective in widening the slit ; in the 

 former, the sporangia being closely united, such mechanical effect 

 would be impossible. 



Though the loculi of a sorus are frequently of nearly uniform size, 

 examples may often be found where they vary to an extreme degree ; 

 and these have an important bearing upon the theory of septation ; 

 for cases of incomplete septation are often to be recognised in the 

 mature sorus, while the study of earlier stages has revealed almost all 

 imaginable steps between the single loculus and two loculi lying side 

 by side as an obvious pair. Such pairs of loculi are common ; some- 

 times the septum between them is of the average thickness ; some- 

 times thin, but still complete, with firm, permanent tissue con- 

 tinuous across it ; sometimes the permanent tissue is incomplete, and 

 the septum composed in its middle part only of tapetum, which dis- 

 appears at maturity ; sometimes a large loculus will be seen with only 

 slight encroachments of tapetum upon the sporogenous group, thus 

 indicating the position, though not realising the complete develop- 

 ment of a possible septum ; the last step of the series would be simply 

 a loculus larger than the average, and these are common. 



An analytical study of the tissues shows that the tissue of these 

 partial septa may have either of two sources of origin : (1) single 

 cells of the sporogenous group are liable to development as sterile 

 cells ; this has been seen in sporangia which even approach the 

 normal ; (2) the surrounding tissue may encroach on the sporogenoiis 

 ^roup, in the form of tapetal cells, which, when their development is 

 considerable, is followed by cells of permanent tissue of the wall ; in 

 these cases the partial septa will be clearly seen in the mature state. 



The similarity between these results and what is known in the 

 case of septate anthers of Angiosperms is of peculiar interest ; in these 

 anthers partial septa are common, and a detailed comparison of them 

 with those of Dancea suggests that the phenomena are closely alike. 



