94 Gelehrte Gesellschaften. 



should have predicted. Mr. Tbiselton Dyer is of opinion that the 

 disease has always been ,hanging about' the Potato. Mr. Baker, a 

 member of tbis Committee, is of opinion tbat ,Any plant brougbt to 

 tbe tuber-bearing State is in a diseased unhealtby condition'. But 

 perhaps it may be found tbat tbis is simply putting the cart before 

 the horse; and that in tbe case of tbe Potato plant we should have 

 no tubers at all except for tbe inroad into its tissues of the Pero- 

 nospora infestans. 



Mr. Worthington Smith's communication (which was not read 

 at the meeting, for reasons before stated), is as follows : 



Wben Mr. A. S. Wilson publisbed bis paper in the Gardeners 

 Cbronicle for October 7, 1872, I wrote at once (October 28) to say 

 that the bodies he had described ,had been familiär to me for many 

 years'. At tbat time I thought I had myself seen Peronospora infestans 

 arising from bodies similar to Mr. Wilson's in autumn. 



The cbief point of interest does not centre in the presence of 

 Oxalate of lime , which is not invariably present. The question is, 

 ,Does tbe Potato fuugus ever really and truly arise from the bodies 

 described by Mr. Wilson'? Mr. Wilson has stated in tbe most 

 detailed and emphatic manner that it does , and I acknowledge that 

 Mr. Wilson's view has support from what I have myself seen. 



The accompanying drawing (fig. 64) is from a mounted micros- 

 copic preparation given to me in 1882 by Mr. Wilson. It shows, 

 enlarged 100 diameters, one of the plasmodium-like bodies, A, naturally 

 divested of its Oxalate of lime. Springing from tbis body is an exces- 

 sively attenuated mycelial thread, which rapidly increases in diameter 

 at H to ten times its first diameter as seen near the ball of proto- 

 plasm. Tbis basal part of the preparation is furtber enlarged to 400 

 diameters at B , to show the extreme tenuity of the mycelial thread 

 and a fold in the feeble cell wall of the ball of protoplasm. The 

 nature of tbis first mycelial growth , A, H, C, may be compared with 

 the familiär pro-mycelium , and from it at D , E, F, G, numerous 

 conidiophores of Peronospora infestans arise. 



The example is in fluid , and the whole basal part moves freely 

 too and fro from the elbow at H, but constant movement has had no 

 effect in detaching tbe ball. 



The explauation of tbis growth may be tbat in tbe autumn the 

 tubers belonging to diseased Potato plants contain the plasma of 

 Peronospora infestans in a free state, or in the state so familiär to 

 US in zoospores. It is there resting, and in tbis resting condition it 

 is carried up into the stems and leaves of tbe Potato plant in the 

 process of tbe Potato plant's growth. The presence of the fungus 

 plasma excites the production of Oxalate of lime in the cells of the 

 Potato plant. When the next autumn arrives the plasma, which tili 

 then had been resting, renews its vitality, bursts through the coating 

 of Oxalate of lime (when there is one) and reproduces the Perono- 

 spora. 



Martius in bis Die Kartoffel-Epidemie, 1842, pl. iü., figs. 19, 23, 

 and 24, has illustrated a peculiar growth in Potatos &imilar as I think 



