268 FUNGI. 
which have followed those grains wherever they have been 
distributed, and the potato disease, which is said to have been 
known in the native region of the potato plant before it made 
its appearance in Europe. We might also allude to Puccinia 
malvacearum, Ca., which was first made known as a South 
American species; it then travelled to Australia, and at length 
to Europe, reaching England the next year after it was recorded 
on the Continent. In the same manner, so far as we have the 
means of knowing, Puccinia Apii, Ca., was known on the Con- 
tinent of Europe for some time before it was detected on the 
celery plants in this country. Experience seems to warraut the 
conclusion that if a parasite affects a certain plant within 
a definite area, it will extend in time beyond that area to 
other countrics where the foster-plant is found. This view 
accounts in some part for the discovery of species in this country, 
year after ycar, which had not been recorded before; some 
allowance being made for the fact that an increased number of 
observers and collectors may cause the search to be more com- 
plete, yet it must be conceded that the migration of Continental 
species must to some extent be going on, or how can it be 
accounted for that such large and attractive fungi as Sparassis 
crispa, Helvellas gigas, and Morchella crassipes had never been 
recorded till recently, or amongst parasitic species such as the 
two species of Puecinia above named? In the same manner it 
is undoubtedly true that species which at one time were common 
gradually become somewhat rare, and at length nearly extinct. 
We have observed this to apply to the larger species as well as 
to the microscopic in definite localities. For instance, Crater- 
ellus cornucopioides some ten years ago appeared in one wood, 
at a certain spot, by hundreds, whereas during the past three or 
four years we have failed to find a single specimen. As many 
years since, and in two places, where the goat’s-beard was abun- 
dant, as it is now, we found nearly half the flowering heads 
infested with Ustilago receptaculorum, but for the past two or 
three years, although we have sought it industriously, not a 
single specimen could be found. It is certain that plants found 
by Dickson, Bolton, and Sowerby, have not been detected since, 
