The Besting Spores of the Potato Fungus. By W. G. Smith. 117 
rapidly about like animalcules. This rapid movement usually lasts 
for about half an hour, and (like the dust-like conidia or " simple- 
spores" before mentioned) the swarm-spores generally enter the 
breathing pores of the leaf, and there germinate. So potent, how- 
ever, is the contents of these bodies when set free, that it is capable 
of at once corroding, boring, and entering the epidermis of the leaf, 
or even the stem or tuber itself. These zoospores are best seen when 
within the vesicle F, where they arise from a differentiation of the 
contents, but when once set free (G) they are, from the extreme 
rapidity of their movements, very difficult to make out. In about 
half an hour they cease to move, their lash-like tails (cilia) disap- 
pear, and having burst at one end, a transparent tube is protruded, 
which is a similar mycelium in every respect with that produced by 
the simple-spore, and which grows, branches, and fruits in a pre- 
cisely similar manner. 
Now the great difficulty which has beset botanists for so many 
years has been to account for the winter life of the Potato fungus. 
Simple-spores and zoospores are lost in the production of the my- 
celium or spawn, and this latter fine thread-like material cannot 
of course survive the frosts and rains of winter, but must utterly 
perish with the perished leaves and haulm. 
A study of other species of Peronospora allied to the one which 
produces the Potato disease, reveals the fact of a third mode of 
reproduction. Simple-spores and zoospores are termed asexual, 
because they are without sex, as distinguished from other bodies 
called oospores, which are produced by the contact of two sexual 
spore-like bodies, known as the antheridium, which is the male, and 
analogous with the anther, H, and the oogonium, the female, and 
analogous with the ovary of a flower, J. The oospores, not till now 
seen for certain in the Potato disease, are the true resting spores. 
Instead of being transparent and unenduring, as are the simple 
and zoospores, these bodies are at length dense in substance,- 
black-brown in colour, and covered externally with reticulations 
or warts. They are produced from the mycelium, by the contact 
of the antheridium and oogonium in the substance of the decay- 
ing plant; they are washed into the earth, and there they rest 
till a certain set of conditions makes them germinate in the year 
following their production, just as a seed falls and rests in the 
autumn and starts again into life during the following spring. 
The terms here used will be better understood if the following 
note is borne in mind : The oogonium is analogous with a pod, the 
oosphere within answers to the ovule, and the oospore (or resting 
spore) is the matured seed. The antheridium with its contents is 
analogous with the anther and its pollen. 
In various other fungi nearly aUied to the Potato fungus these 
resting spores have been seen, measured, and illustrated, but till 
