OP ARTS AND SCIENCES. 13 



II. 



PRELIMINARY KOTES ON THE SPECIES OF 

 DOASSANSIA, Cornu. 



By William Albekt Setchell. 



Presented March 11, 1891. 



The genus Doassansia was established by Cornu, in 1883,* to 

 receive the Sclerotium AUsmatis, Nees, on Alisma, and a new species, 

 D. Farlowii, on Potamogeton. Since then there have been several 

 additions both of old and of new forms, until at present the number 

 of species referred to it is twelve. All of them inhabit hosts which 

 are more or less aquatic in habit, though belonging to widely sepa- 

 rated families. They are said to differ little" in structure, but to be 

 distinguished from one another chiefly by the differences of the host 

 plant.f A careful study of the species distributed in the various 

 " Exsiccati," as well as of the accessible living material, has shown 

 that this is not strictly correct. Not only are most of the species 

 fairly well characterized by peculiarities of structure, but there are 

 also several types of structure sufficiently diverse to be given sub- 

 generic or even generic rank. Moreover, by the discovery of sev- 

 eral new species, additional types of structure have been found, and 

 have rendered it even more necessary that a careful revision of all 

 the species should be made. On this account, full descriptions and 

 figures of all the specias of which material was available have been 

 prepared, but as there is a delay in publication, it has seemed best 

 to give a brief summary of the results in the present preliminary 

 notice. 



The spores of the Doassansice resemble those of the species of 

 Entyloma both in structure and in germination ; but in the former 

 they are collected and compacted into balls, called by most writers 

 " sori." The species of the genus Doassansia have in addition a coat, 

 or "cortex," of sterile cells surrounding the sorus, Cornu certainly 



* Ann. Sci. Nat., ser. 6, Tom. XV. p. 285. 



t Cf. Schroeter, Pilzfl. Schles., p. 286, 1887. De Toni, Journ. Myc, Vol. 

 IV. p. 14, 1888. 



