184
THE ESSEX NATURALIST.
wax-like appearance when wet, resinous when dry,
diameter of hyphal thread .06 mm. Radially elon-
gated cells form a complete circle under the mantle.
(2) Brown, branches approximately distichous; diameter
.4 mm.; exterior of fungoid mantle smooth. Radially
elongated cells form an incomplete circle.
(3) White in colour, coralloid branches short; diameter
.5 mm.; fungoid mantle shaggy with loose hyphae.
No radially elongated cells.
(4) Yellowish-brown, branches often shorter than the
distances between them, widely scattered, mostly uni-
lateral; diameter .3 mm. or less, fungoid mantle more
or less shaggy, attached to the finest attenuated root-
lets.
The above descriptions must be considered as approximate
only for average mycorrhiza, for it is apparent that the fungus-
root is considerably modified by the temperature and rainfall
at the time of its formation.
It is interesting to note that the stigmas of the birch flower
remain upon the fruit until it falls in September, and even until
the seed germinates. Before its fall hyphal threads are present,
twisted around the separate styles and passing in loose coils
from one to the other. The presence of the fungus there is not
easy to explain. It was noticed on a very large percentage
of the fruits in September, 1921, at the end of a phenomenal
drought, so that from the first it was quite clear that it is not
there as the result of a period of very damp weather. The expla-
nation that suggested itself was, that the fungus was living
on the tissues of the style, but one could not altogether disregard
the fact that on germination the radicle would have to pass
between the hyphae on emerging from the seed-coats.
Seeds germinating under observation have revealed exactly
what takes place, for after the radicle has passed through the
hyphal barrier, the hypocotyl, which is studded with a multitude
of minute hooked processes, all pointing in the direction of the
growing point of the root, that is, downwards, follows. Some of
these hooks catch on the hyphal threads and carry them to the
upper surface of the soil. At the point of junction of the hypo-
cotyl and the radicle there is an accumulation of hyphae belonging
to various species of fungus, among which are those that have