AIARATTIACKAK 



519 



have been noted also in other genera, so that Danaea does not stand 

 alone, though the demonstration is most effective in that genus. 



In putting a morphological interpretation on these facts it is to be 

 remembered that the genus Danaea has in many of its species very 

 long sori compared with those of Marattia, External comparison had 

 already suggested an elongation of the type of the latter genus to produce 

 the sorus of Danaea. The internal structure is now seen to be conform- 

 able to such a progression, for the partial septations are commonly 

 found in those sporangia which are larger than the normal : they thus 

 appear to have followed upon expansion of the sporangia. Their existence 



Fit;. 287. 



Pecopteris{Dacty[otheca) dcntata. Part of a frond with the Matrix. Reduced after a 

 photograph by Mr. W. Hemingway. From Scott's Studies in Fossil Botany. 



here, as well as occasionally in other genera, raises the question whether 

 or not septation has been effective in the primary production of the 

 sorus : this will be considered again later. 



The synangial sori differ from those with separate sporangia in the 

 mechanism which accompanies dehiscence, though the dehiscence itself is 

 uniformly by a radial slit. The annulus represented in Angiopteris by a 

 broad indurated band or hoop, is absent : clearly it would be useless in 

 a synangium, for it could not possibly be effective unless the sporangium 

 were free from mutual relations with others. In Kaulfussia and Danaea 

 the radial slit of each sporangium may widen as the neighbouring cells 

 dry up, to form an almost circular pore. In Marattia there is in addition 

 to this a change of form of the whole sorus at maturity : its two sides, 

 originally in close juxtaposition so that the distal ends of their sporangia 

 almost touched, move apart like the opening of a book. In Danaea 

 and Marattia the whole external wall of the synangium is composed of 

 deep indurated cells : the condition of Angiopteris appears accordingly 



