110 The Besting 8]pores of the Potato Fungus. By W. G. Smith. 
objective, and nearly parallel with the stage, the microscope being 
in an upright position. 
My present impression, which is open to correction, is that the 
winter rays of the sun strike obliquely on the upper surface of the 
slide, and some of these being reflected, pass through the object at 
an oblique angle, and cause the same appearance as if the object 
were illumined by light transmitted from the mirror, 
Adelaide, South Australia. 
m, — The Besting Spores of the Potato Fungus. 
By WoRTHiNGTON G. Smith, F.L.S. 
Plates CXIV., CXV., and CXVI. 
The Potato disease in this country is rarely seen before the month 
of July, but this year I received some infected leaves for examina- 
tion from the Editors of the * Journal of Horticulture ' at the 
beginning of June, and my reply to the correspondent was printed 
on June 10. The leaves were badly diseased, and I detected the 
Peronospora in very small quantities here and there, emerging 
from the breathing pores. This was a week or ten days before Mr. 
Berkeley brought the matter before the Scientific Committee of the 
Eoyal Horticultural Society ;* and when I heard Mr. Berkeley's 
remarks about the Protomyces, I immediately accused myself of 
great carelessness in possibly overlooking it ; but I was equally 
certain of the presence of the Peronospora in the specimens I 
examined. 
On receiving authentic specimens of diseased plants from Mr. 
Barron of Chiswick, the brown spots on the Potato leaves at once 
reminded me of the figures of some species of Protomyces, and the 
dimensions agreed tolerably well with some described plants of that 
genus ; but the spots, when seen under a high power, appeared very 
unlike any fungus, and they were very sparingly mixed with other 
bodies much smaller in diameter, and with a greater external 
resemblance to true fungus spores. These latter spore-like bodies 
were of two sizes — one transparent and of exactly the same size as 
the cells of the leaf (and therefore very easily overlooked), and the 
other darker, possibly reticulated, and smaller. A few mycelial 
threads might be seen winding amongst the cellular tissue, and 
these threads led me to the conclusion that the thickened and dis- 
coloured spots on the leaves were caused by the corrosive action of 
the mycelium, in the same way as Peach, Almond, Walnut, and 
other leaves are thickened, blistered, and discoloured by the spawn 
* See ante, vol. i., 1875, p. 795, 
