128 The Besting Spores of the Potato Fungus. By W. G. Smith. 
if not the same, some close ally with mine, even if it should turn 
out to be a true Pythium, and its oogonia produce zoospores in 
water, especially after what is known of the nature of Cystopus, the 
close ally of Peronospora. Two strong points in favour of this 
view are these : (1) The resting spores of Pythium are unknown, 
but if I find Pythium inside Potato stems and leaves mixed up 
with the Peronospora, and the same Pythium in the very centre of 
the tuber of the Potato (as I have done), there maturing itself and 
forming its resting spore, then the identity of the two may reason- 
ably be assumed, and the resting spore of the Pythium, as well as 
the Peronospora, is found. (2) The same cells in the Saprolegnieae 
will alternately produce, under the same (or different) conditions, 
zoospores or resting spores ; therefore, if zoospores are produced 
in Mr. Kenny’s oogonia in water, it is reasonable to assume 
that under different conditions resting spores would be formed by 
similar cells. I have, from the first, believed the Saprolegnia con- 
dition of the fungus to be widely diffused, and when in that state it 
quite possibly grows on diverse plants and substances in watery 
places, as was explained by me. The Saprolegnia is the caterpillar 
condition (belonging to the water, like the larva of the dragon-fly), 
the Peronospora somewhat analogous with the perfect butterfly, 
and the resting spore with the dormant chrysahs. 
5. I find by experiment, when badly diseased haulm, fruit, and 
tuber are partly submerged for from one to four days, the Perono- 
spora changes its character, and produces the Pythium or Sapro- 
legnia-like growth on the submerged parts. On examination of 
the plants this may be easily overlooked, as the Saprolegnia 
commonly frees itself and floats on the surface of the water, and 
must be carefully taken off (invisible as it is) with a camel-hair 
pencil. If the oogonia now produce zoospores in the water, as in 
Pythium, which is possible and even probable, it in no way invali- 
dates my views, or makes the connection less probable between 
Pythium and Peronospora. 
6. The aerial spores of the Peronospora never become globular 
in water, whilst the oogonia and antheridia are always so. 
7. A superabundance of water excites the growth of the 
mycelium, but it retards the proper production of the resting 
spore, just as a superabundance of water in most plants makes 
leaves and retards flowers. 
8. In my calendar of the weather I find we had here only five 
wet days from May 7 to June 10 (no wet between May 8 and 20), 
and it was during this dry weather that the Potato fungus this 
year lived inside, and at the entire expense of the plant, and there 
perfected its resting spores. With the twenty-two wet days after 
June 10 the Peronospora put on its usual shape, and came to the 
surface. 
