The Potato Fungus. By Worthington G. Smith. 125 
became dense and dark, with the oospore occupying the whole of 
the oogonium as at I ; this condition is different from that of the 
body A, for in this the resting spore, being not quite mature, does 
not yet occupy all the oogonium, but floats within from side to 
side, as the object happens to be moved under the microscope. 
J shows the contents of oospore being broken up into zoospores ; 
K shows the zoospores within still more clearly, and where they 
are giving an echinulate appearance to the bladder within (an 
appearance adverted to lately by Mr. Berkeley in a letter to the 
* Gardeners' Chronicle'); L shows the bladder from within the 
oospore being discharged from the oogonium after the manner of 
Cystopus, with the contained zoospores; this bladder frequently 
breaks up into dust, as at M, setting the zoospores which are at 
present quiescent free, as at N ; two tails shortly appear on these 
latter bodies, and at a certain period of their growth the anterior 
cilium, or tail, is pushed straight out as seen at 0, the posterior 
tail then quivers with an undulatory movement, and the zoospores 
sail out of the field of the microscope. How long the zoospores live 
it is difficult to say, but probably somewhere between twelve hours 
and a week ; at length they come to rest, as at P, when the tails 
fall into fine dust. Some zoospores burst and at once perish, as at 
Q, whilst others throw out threads of mycelium, E, which threads 
are destined at length to bear the conidiophores of the Potato 
fungus in its new generation. The zoospores thus obtained were 
planted on the foliage, and upon thin slices of Potato supplied from 
a frame by Mr. Alfred Smee. On these materials they at once 
produced mycelium and small conidiophores, which, without doubt, 
belonged to Peronospora, but as better results were afterwards 
obtained from resting spores similar to I, Plate CLI., the figures 
are not here engraved. 
The Eev. J. E. Vize, Forden Yicarage, Welshpool, a gentleman 
who has made a special study of microscopic fungi, has had some 
of my living material under examination during the past winter 
and spring, and when the first signs of germination showed them- 
selves in my oospores, I wrote him to keep a good look-out for 
results. He wrote me as follows, under date of April 21 : " My 
idea certainly is that the oospores are germinating : bottle No. 1 
had a thin film on it which developed into a lot of mycelium 
and threads of Peronospora ; " I too observed the same fact in 
London. 
Throughout May the habit of the oospores appeared to remark- 
ably change, for instead of producing zoospores they protruded a 
thick and generally jointed thread, this thread agreeing exactly in 
size with average Peronospora infestans threads. On May 13 I 
observed on the preparations treated with expressed juice of horse- 
