28 
SAPROPHYTES AND PARASITES 
special substance normally present in the cells of the 
njected plant. 
By experiments of this kind true saprophytes have been 
transformed into parasites, showing that parasitism is an 
acquired habit. 
I am not acquainted with any statistics giving the annual 
loss to foresters through the ravages of parasitic fungi; it 
must be very great. Prussia is said to have lost more than 
^20,000,000 in the year 1891 through an epidemic of grain 
rust. The United States Department of Agriculture stated 
that the losses in 1897 through injury caused by fungi 
amounted to about ^"40,000,000. This enormous sum prob¬ 
ably includes damage to forests as well as to cereals and 
fruit. 
One of the commonest of our native fungi, and a deadly 
enemy of conifers, Fomes annosus , forms the subject of 
Plate XII. It is a perennial, depositing a new stratum of 
tubes every year over the old ones (Plate XII., 2), which 
die and become very hard. These are best seen in large 
sporophores growing out of erect trunks (Plate XII., 1). It 
encrusts anything with which it may come into contact, and 
often occurs with leaves and twigs embedded in it. I have 
a sporophore which was found with a living shell (Helix 
rotundata) protruding from, but firmly fixed to, the hymenial 
surface. When growing on roots it is often quite adnate 
(Plate XII., 6). It frequently appears in this state on 
roots exposed in rabbit burrows; the spores fall upon the 
fur of the passing mammals, and are brushed upon the roots 
of other trees. The hyphse enter between the bark of the 
root, and form a white felt of mycelium, which creeps up¬ 
wards into the trunk, appearing like little white balls 
through any cracks which may occur in the root bark 
(Plate XII., 3). The mycelium slowly spreads up the 
middle of the stem, destroying its tissues and hollowing it 
out like a pipe. Plate XII., 5 depicts the section of a 
