560 Scientific Proceedings, Royal Diiblin Society. 



Phytophthora, and that those which follow the Cacforum-type should be 

 placed in a new genus for which the name Nozemia is suggested. Some other 

 species usually included in the old genus Phytophthora, the development of 

 whose sexual organs is as yet unknown in detail, cannot at present be 

 assigned with certainty to either of these genera. 



(8) Tlie genus Phytophthora as amended is to be removed from the 

 family Peronosporaceae, and is to constitute the sole member, at present, of 

 the family Pliytophthoraceae. 



(9) The disease is prevalent in the west of Ireland, and the losses caused by 

 it are considerable, in some cases being greater than those diie to P. iiifestcms. 

 They are greatest in crops grown continuously on the same land (infection 

 taking place from the soil), and can be avoided by a proper rotation. 



(10) Tlie disease is probably transmitted to some extent by oospores 

 which adhere to the external surface of the seed tubers, but the rot is too 

 rapid to admit in practice of its transmission internally in the form of 

 mycelium within them. 



Addendum. 



While this paper was ])assing though the press, further information was 

 obtained with regard to the behaviour of the species P. Faberi, P. Nicotianae, 

 and P. Jatrophae when grown in pure cultures. 



P. Faberi grows well on neutral wort gelatine, carrot extract agar and 

 gelatine, Quaker oat agar and gelatine, and but poorly on oat-juice agar and 

 Salep agar. On some of these media conidia are produced fairly abundantly 

 (Salep) ; on others they are rarer or entirely absent. On an agar medium 

 made from extract of cocoa shells, conidia are developed plentifully, and when 

 transferred from this to tap water they germinate rapidly and produce 

 zoospores. In cultures on carrot extract agar, a few yellowish, more or less 

 pear-shaped, bodies have been observed, ranging from 27 to 43^ iu diameter, 

 and having fairly thickisli walls. These bodies may possibly be ill-developed 

 oogonia ; but no signs of antheridia have been seen accompanying them. 



P. Nicotianae and P. Jalropliae appear to resemble one anotlier rather 

 closely when grown in pure cultures. A few conidia have been observed in the 

 case of the latter, but none iu that of the first-named. In both of them rather 

 large,spherical, spore-like bodies have been observed, having diameters ranging 

 between 15/^ and 39^. The thickness of the walls of these bodies varies 

 from 0-9 to 1'8/x in Nicotianae and from 1 to 2-5/i in Jatvophae. They are 

 in most instances intercalary, and usually rather near the end of ahypha; 

 but some of them appear to be terminal. Tliey are, perhaps, to be regarded 

 as bodies of the nature of chlamydospores, for they do not resemble oogonia 

 with oospores within them, and no signs of antheridia have been seen. 



