322 BOTANICAL GAZETTE [NOVEMBER 
stock. There are also interesting examples of a shift from one host 
to a host of another related genus, instead of to a species of the same 
genus, where in the migration the specific hosts are not evenly dis- 
tributed over the area of general migration from a given region. 
Pleurotus ulmarius Bull., while occurring on other frondose trees, 
is more common on the elm both in Europe and North America, 
although our native species of elm is different specifically from the 
European elm. Annularia jenzlii Schulz. was first collected in 
Hungary on Tilia ewropaea and does not seem to be common or widely 
distributed in other parts of Europe. It has been collected once at 
Ithaca, N. Y., on our native species of basswood, Tilia americana. 
Fomes fraxineus (Bull.) Fr. seems to be confined to the ash, occurring 
on the European ash in Europe and on our native species in the 
United States. Fistulina hepatica (Huds.) Fr. occurs in Europe 
especially on the oak, but sometimes on beech and chestnut. In 
North America it occurs most commonly on the chestnut, but is 
reported also on the oak, European species of oak not occutting 
naturally in this country. Many other similar examples might be 
enumerated. In a number of cases the fungus species seems to have 
undergone little or no change, although now separated for centurie 
on two different continents and subjected often to widely different 
environmental conditions, In other cases the North American repre 
sentative of European species seems to have undergone 4 change, 
Whether gradual or sudden we cannot say, so that it presents certain 
constant characters worthy often of specific separation, while resem- 
bling in a striking way the European species. 
One of these interesting problems is presented by Poly ah 
lucidus Fr.? (Boletus lucidus Leys.3). My first acquaintance with 
What appears to be the typical form of P. lucidus in Europe os 
the autumn of 1903, when I collected a specimen growing from - 
Toot of a dead frondose tree in the Bois de Boulogne, Paris. Two 
eg later, while visiting M. E. Bouprer at Montmorency, — 
Paris, he gave me a fresh young specimen which had been sent 
from one of his numerous correspondents in France. It is a large 
cae handsome fungus, varying considerably in size and form. The 
typical forms are stipitate, with a lateral pileus. In these ae 
? Flora Halensis 300. 1783. 3 Syst. Myc. 1:353- 1821- 
