Pethybeidge — On the Rotting of Potato Tubers. 559 



Attention to these points probably explains why this rot has not yet been 

 found to cause serious trouble iu districts wliere good methods of farming 

 *re in vogue. 



VIII. Summary. 



(1) In the introductory part of this paper a brief resume is given of the 

 literature dealing with the principal forms of rot previously kuown to occur 

 in the potato tuber. 



(2) A detailed description is given of a new form of rot, for which the 

 name Pink Eot is suggested, caused by a hitherto uudescribed species of 

 Phytophthora to which the name P. erythrosejitica is given. The rot is a 

 rapid one, and on the whole would be called a wet rather than a dry one. 

 Tiie cut surfaces of affected tubers quickly turn pink when exposed to the 

 air, and later become almost black. 



(3) An account is given of the methods by which the fungus was obtained 

 in pure culture, and proved to be pathogenic to the potato and to some other 

 plants. 



(4) The characters of the fungus are described in detail, the method 

 of development of the sexual organs being peculiar and novel. The oogonial 

 incept enters the antheridium at or near its base, grows up through it and 

 out at the top, expanding there to form the oogonium proper in which the 

 oospore develops. It is not certain whether fertilization occurs, but if so it 

 would appear to take place before the formation of the oosphere. 



(5) The production of oospores and couidia has not yet been seen in or on 

 the potato tuber itself, but an account of the growth of the fungus and the 

 development of these bodies on various media is given. It can be cultivated on 

 these media much more readily than its near ally P. infestans. It would 

 appear that the production of oospores is inhibited by acid, and that the conidia 

 are usually produced only under water. 



(6) The characters of the fungus are compared with those of other 

 members of the genus Phytophthora. It has been found tliat P. infestans 

 de Bary and P. PhaseoK Thaxt. agree with P. erijthroseptica in the manner 

 in which the oospores are produced, while it is highly probable that 

 P. omnivora var. Arecae Coleman will be found to follow the same mode of 

 development. 



The sexual organs of P. Cactorum Schroet. Poronospora Fagi Hartig 

 (P. omnivora de Bary) and Phijtophthora Syringae Klebahn are developed in 

 the manner described by de Bary for his P. omnivora, which is usually 

 regarded as typical for all species of Phytophthora. 



(7) It is suggested that only those species whose sexual organs are 

 developed according to the in/estans-type should be retained in the genus 



