BULLETIN OF THE BUSSEY INSTITUTION. 393 
which attack decaying substances, and are found on potatoes as well 
as on a great many other substances. Fig. 6 is the fungus known as 
Mucor stolonifer De Bary (Rhizopus nigricans and Ascophora mucedo 
of many writers), and is particularly common on bread. Fig. 7 repre- 
sents the mycelium and asexual spores of Penicillium crustaceum, Fr. 
(P. glaucum of other writers), which is the common blue mould found 
on most articles of food. 
The potato rot is a totally different thing. Here we have a fungus 
which attacks the potato plant while it is yet alive, and the crop is 
destroyed either by a direct invasion of the tubers by the mycelium of 
the Peronospora, or by the destruction of the tops before the tubers 
have attained a sufficient size. When the potato plant dies, the 
Fie. 6. Fig. 7. 
Peronospora which has destroyed it, dies with it; but, after it is dead, 
it may still be attacked by some of the decomposition moulds before 
mentioned and by insects. 
Whatever science may have to say, no season during which the rot 
has prevailed to any extent ever passes that some cultivator of potatoes 
does not proclaim to the world that he has discovered that the disease 
is caused by insects, and offers, as proof, the fact that he has found 
insects on some rotten potatoes. The mere fact that insects are found 
on rotten potatoes does not prove any thing whatever as to the cause 
of the rot. It is quite as logical to infer that the rotten potatoes pro- 
duced the insects as that the insects produced the rot. To prove the | 
point, one should have found the insects on healthy potatoes, and have 
noticed that the rot always followed their visits, and did not appear at 
other times. ‘Those who think there is something in the insect theory, 
and this number certainly does not include any entomologist, do not 
