THE FUNGUS-ROOT (MYCORRHIZA). 181
abundant. It is perhaps well to note that during the past six
weeks (February—March 1923) there has been an abnormal
fall of rain and very slight frost in the south eastern counties.
This may account for the abundance of mycorrhiza. A remark-
able phenomenon was witnessed by members who were present
at the Club's Moss Foray on March 17th, 1923. In a hollow
of considerable size where beech leaves had accumulated there
was, within an inch of the surface of leaves, a complete carpet of
mycorrhiza, several layers in thickness. Not a single rootlet
appeared to be in a normal condition. The exact dates
given above are of some importance for we have not yet sufficient
data as to the length of life of mycorrhiza after once being formed.
McDougall,4 in describing the result of his investigations,
writes, "The primary object from the beginning was to work
out the seasonal relations of the mycorrhiza of our forest trees."
"Both ectomycorrhiza and endomycorrhiza are normally
annual. They are formed during the summer, reach their fullest
development in late autumn, persist unchanged throughout
the winter, and die in the spring."
The climatic factor appears to be the chief determining
one in causing the changes stated above.
To obtain the mycorrhiza of a birch tree that is growing in
its customary oak-birch-heath association, all that it is necessary
to do is to remove carefully to the depth of from one to two inches
the upper surface of accumulated dead leaves, in which the slender
root system of the tree is always present.
Mycorrhiza break off very easily, part with the moisture they
contain, and shrivel, becoming almost unrecognisable, on being
exposed to an atmosphere that is at all dry. It is advisable,
therefore, not to put them into a vasculum with other plants.
They should be packed in wet moss or put into water in wide
mouthed bottles of two-ounce capacity. If at the time of collecting
they can be rinsed in a pool or stream of slowly running water,
characteristic points, that it is important to know, as colour,
shape and size, may be ascertained at once. Other methods are
required when collecting from trees having a deeper root-system,
such as oak and hornbeam. With these the soil has to be removed
little by little to prevent undue injury. A recent writer recom-
4. Mc. Dougal, W. B., "On the Mycorhiza of Forest Trees." Americ. Journ. Bot., i., pp.
51-74 (4 pls.), 1914.