556 Scientific Proceedings^ Royal Dublin Society. 



P. agaves, and P. Jatrophae), the remaming species included at present in the 

 genus Phytophthora fall naturally into two groups, which differ markedly in 

 the manner in wliieh the sexual organs are developed. Using tlie names of 

 the oldest species in each of these groups, the latter may be referred to as the 

 Cactoruiii-grou^ and the infestans-gvou'p respectively^ 



In the species belonging to tlie Cadorum-gronTp, viz., P. Cadomm, P. Fagi. 

 and P. Syriiigae, the sexual process is the well-known one common to the 

 family Peronosporaceae. In P. Nicotianae, which should probably be included 

 here also, it is stated that tlie whole of the contents of the antheridium passes 

 into the oogonium at the time of fertilization, as in Pythium. 



In the species belonging to the infestans-gvoVi^, however, the sexual process 

 follows that described for the first time in the present paper. The members 

 of this group are P. erythroseptica, P. infestans, P. Phaseoli, and (doubtfully) 

 P. Arecae. 



The sexual process in this latter group is such an exceptional one that 

 its occurrence in certain members of the genus, and its absence in others, 

 appear to me to cause tlie generic name, Phytophtliora, to embrace "elements- 

 altogether incoherent,"^ having regard to those characters which are com- 

 monly accepted as being of sufficient import for use in the classification 

 of the Phycomycetes. Hence it seems necessary to separate these groups, 

 and to place them in different genera. I propose, therefore, that tlie generic 

 name, Phytophthora, be retained for those species alone which belong to 

 the infestans-group, as defined above ; and I consider that this genus is to 

 be withdrawn from the family Peronosporaceae, and must find a place as the 

 sole representative, at present, of a new family, the Phytophthoraceae. 



The amended description of the genus Phytophthora (based on the 

 diagnosis given by Saccardo) would then run as follows : — 



Mycelium in cellulas matricis, quas enecat, haustoriis sparsis vel nuUis 

 iustructum. Hyphee conidiophoree plerumque parum ramosse. Conidia 

 primo acrogena dein etiam pleurogena, ovata, apice nonnunquam papillata 

 zoosporipara vel hyphaepara. Antheridia terminalia aut lateralia aut 

 intercalaria rotunda aut ovoideia penetrata ad vel juxta bases suas oogouiis 

 incipientibus quae deinde ex partibus summis emergunt. Oogonia 

 pyriformia partes inferiores intra antheridia superiores autem in summis 

 autheridiis habentia. Oosporse sphajricse erasso episporio prseditse. 



For the species belonging to the Gactorum-gm\n^ I propose the new generic 

 name, Nozemia, and characterize the genus as follows : — 



Mycelium in cellulas matricis, quas enecat, haustoriis sparsis vel nuUis 



' International Rules ol Bot. Nomenclature, 1912. Art. 51 (4). 



