338 SEXUAL EEPRODUCTION OF PERONOSPORA INFZSTANS. 



vol. viii., tab. mccxi. See also "Flora of Essex," p. 266. I hope 

 to give soon a figure and full description of this interesting species.— 

 Henrt Tkimen". 



oKrtract^ anb 3llB^trncts?. 



THE SEXUAL REPRODUCTIOX OF PERONOSPORA 

 mFESTANS, MOI^T. 



"Wr have been favoured by the proprietors of the *' Grardener's 

 Chronicle" and ''Journal of Horticulture" with the carefully-drawn 

 figures illustrating Mr. "Worthington Smith's observations on the 

 resting-spores of Peronospora infestans, to which allusion has been 

 made on p. 242. Referring to the "Gardeners' Chronicle" for this 

 year (pp. 35, 46, 68, and 101) for the details of the successive steps 

 in Mr. Smith's investigations, it will sufficient here to describe the 

 figures. 



The antheridia and oogonia are circular transparent bodies borne 

 upon the mycelium in the interior of the structure of the Potato- 

 plant. They have been detected in the leaves, stem, and tubers, and 

 though very sparingly found at the commencement of the examination, 

 by maceration of the Potato in water they were produced in abundance 

 on the mycelium, the growth of which in the then putrid Potato- 

 plant was Very vigorous. In the accompanying illustration (fig. 1)^ 

 which is an exact copy of the first sketch taken, the two bodies are 

 seen in the substance of the leaf and in contact at JH. The oogonia 

 are almost precisely the same size as the cells of the leaf (B), the anthe- 

 ridia very much smaller. In fertilisation the antheridium sends a 

 fecundating tube (pollinodium) into the wall of the oogonium. In 

 fig. 2 many more of the same bodies are shown, some in actual con- 

 tact. The two upper figures (K L) show the young resting-spores 

 some time after fertilisation, when a coat of cellulose is the result. In 

 K the spore is surrounded by this coat, whilst at L the spore is 

 accidentally washed out by maceration in water. The serai-mature 

 resting-spores shown at M are furnished with a dark coat or skin 

 which, when further maturity is reached, clearly resolves itself into 

 two layers. The antheridia are shown at NN". 



In fig. 4, which represents a transverse section through a black 

 spot in the leaf, the mature resting-spore is seen (A) nestling among 

 the cells of the leaf; the bodies are generally in these spots, but it is 

 a difficult matter to get them out, or even to see them, for they are 

 only a little larger than the leaf-cells, which have become intensely 

 black-brown in colour, and almost as hard as wood. When examined 

 the resting-spore is seen to be about Tni^n inch in diameter, beautifully 

 regular and perfect in outline, spherical or slightly ovoid, and covered 

 with warts or coarse reticulations ; when young they are of a pure warm 

 sienna colour, when perfectly mature brown-black and shining. 

 E is a semi-mature resting-spore with pollinodium attached, acci- 



