468 



MB. T. JOHNSON ON THE SYSTEMATIC 

























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The isolated position of the undivided spores in Dictyopteris and 

 Spatoylossum is, too, a strong argument against a Floridean 

 affinity. Eeinke suggested, in 1878*, that fertilization may 

 take place before the undivided spores have left the thallus, the 

 male corpuscles being passively brought into contact with the 

 oogonia, and exercising their fertilizing-power through the 

 enveloping oogonium membrane, as in the Banqiacece. It is not at 

 all difficult to find the undivided spores escaping as quite naked 

 spherical non-motile bodies, without any signs of a preceding 

 attachment of the male corpuscles. Further, Thuret found 

 that it was only with considerable difficulty the escaped spores 

 in Dirty ota could be made to germinate, and that the seedlings 

 died in the course of a few days. Thuret's observations thus 

 tend to show that the undivided spores are not the products of fer- 

 tilization ; and that if oospheres, they are not parthenogenetic. 

 There is everything to indicate that the undivided spores in the 

 Dictyotacea are oospheres, that in Dictyota and several other 

 genera there are oogonia in sori, that in Dictyopteris and Spato- 

 glossum there are oogonia unilocular and isolated, and that ter- 

 tilization, as yet not seen, takes place in the Dictyotacea, as in all 

 Phceophycea in which it is known, externally y — 1\ e. after the 

 oospheres have become quite free from the thallus producing them. 



Briefly summarizing, it will be seen that : 



1. In their apical growth, 



2. In the parenchymatous manner of formation of the thallus, 



3. In the secondary thickening, as seen in the stalk of Dictyo- 



pteris and probably Zonaria, 



4. In the brown pigment, 

 In the presence in the undoubted Phaophycece, the Tilopte- 



ridce, of potential tetraspores very comparable to the tetra- 



5. 





spores of the Dictyotacece, 



6. In the parenchymatous structure of the antheridia and in 



the male corpuscles, to omit all mention of the possibility of 

 cilia, 



7. In the presence of isolated scattered oogonia in Dictyoptcn* 



and Spatoylossum, 

 the Dictyotacece possess characteristics which are not otherwis 

 peculiar to the Floridece, that, in fact, they are true Melanopty cea ' 

 , I hope I shall not be considered presumptuous in going a ste P 



« Eeinke, in • Nova Acta Leop.-Carol.' (1878) p. 48. 



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