xxxvi.] POTATO DISEASE, I L PASSIVE STATE. 303 



observations upon the potato fungus for that Society. It 

 appears that Professor de Bary also lighted on what he 

 considered to be a fourth new species of Pythium, and 

 first seen by him in potatoes in 1874 and 1875. This 

 fungus the professor named P. vexans, and an original 

 description, with an illustration, is given in the Journal 

 of the Royal Agricultural Society for 1876, vol. xii. p. 252. 

 In 1881, in the Beitrage zur Morphologie und Physiologie 

 der Pilze, Professor de Bary has compared Artotrogus with 

 two other species of Pythium, both new, and named by 

 him P. micracanthum and P. megalacanthum. He says 

 the former may perhaps be Artotrogus. 



It does not specially concern us here what these six 

 species of Pythium are, or whether they are new or dis- 

 tinct from each other or not. P. proliferum, D.By., is 

 probably distinct, but we can see no difference between 

 P. incertum, Ky., P. Equiseti, Sdbk., and P. vexans, D.By. 

 They are simply referred to here because some writers 

 have at times confused the potato oogonia seen by us 

 with one or other of these six organisms. 



As P. vexans, D.By., appears to us to be the same 

 with P. incertum, Ky., and P. Equiseti, Sdbk., we here 

 reproduce at Fig. 132 the original illustration altered to 

 400 diameters for comparison with the Peronospora 

 oogonia given to the same scale in Figs. 130, 134, 135, 

 and 136. It will be noticed that the Pythium is smaller 

 in all its parts, and that the oogonia AAA are invariably 

 non-echinulate. The mycelium is thick and septate in 

 the Peronospora, and non- septate and very thin in the 

 Pythium. 



The great point of difference is this: the Pythium 

 oogonia will, as soon as formed, and within twenty-four 

 hours germinate in water. In germination, a tube is some- 

 times produced, as at B, Fig. 132. In other instances when 

 the oospores of P. vexans, D.By., are kept for a few days 

 so as to ensure their complete maturity, they germinate by 

 ejecting a small transparent bladder, as at C ; the proto- 



