THE RESTI^TG-SrORES OF THE POTATO DISEASE. 19 



both bodies in situ ; and my observations lead me to think that 

 conjugation frequently takes places after both organs are quite free. 

 The antheridia and oospores are best seen in the wettest and most 

 thoroughly decomposed portions of the tissue of the decomposing 

 tuber, but they occur also in both the stem and leaf. I consider 

 Mr. Alexander Dean's remark, as reported in " Gardeners* 

 Chronicle" for June 19 last, p. 795, to have a distinct bearing on 

 this point, where he says : — " In all cases where the seed tubers 

 were cut they were quite rotten." 



Before I referred to De Bary's measurements of similar organs 

 in other species of Peronospora, I was disappointed with the results 

 of my observations, and felt disposed to refer the bodies and threads 

 in the potato leaves to Saprolegnia, but a glance at the figures 

 which I shall shortly j)ublish, and the similar figures copied from 

 De Bary to the same scale, will show that if the bodies observed 

 by me are Saprolegnia-like, the oospores and antheridia figured by 

 De Bary show an exactly similar alliance. Still, as the Sapro- 

 legnie£e are at present defined, I am by no means inclined to 

 describe the bodies observed by me as really belonging to that 

 tribe of plants. 



The Saprolegniese have the habit of moulds and the fructifica- 

 tion of Algae, and they live on organic matter, animal and vegetable, 

 in a state of putrefaction in water. One of the best known of these 

 plants is Botrytis Bassiana, the parasite which causes the disease 

 of silkworms. Now the genus liotrytis amongst fungi is almost 

 or quite the same with Peronospora, to which the Potato disease 

 belongs ; and I consider it a strong argument in favour of my 

 Saprolegnia-like bodies being the oospores and antheridia of the 

 Peronospora when such an authority as Mr. Berkeley (" Micro- 

 graphic Dictionary," p. 6) considers one of the Saprolegnieee 

 (Achlya) " may be an aquatic form of Botrytis Bassiana'' — the 

 silkworm disease. 



The common fungus which attacks flies (so frequently seen on 

 our window-panes in autumn), Siwvendonema muscce, Fr., is said 

 to be a terrestrial condition of Saprolegnia ferax^ Kutz., which 

 latter only grows in water ; and if a fly infected with the fungus 

 be submerged the growth of the Saprolegnia is the result. It would 

 now seem to be somewhat the same with the potato when diseased, 

 in the fact that when submerged a second form of fruit is produced. 



Between the two moulds, Botrytis and Peronospora, there is little 

 or no diff"erence ; the characters of Corda, founded upon the con- 

 tinuous or articulate filaments, cannot be relied upon, and even De 

 Bary himself figures P. infestans with articulate filaments, like a 

 true Botrytis. . The intimate connection, however, between the 

 Saprolegniete and some moulds cannot be denied, as the instances 

 above cited clearly show ; and I am therefore disposed to think 

 that the fungus which produces the potato disease is aquatic in one 

 stage of its existence, and in that stage the resting spores are 

 formed. 



