no Rayner.—Obligate Symbiosis in Calluna vulgaris . 
The ovary of Calluna is four-chambered, each loculus containing 
a number of anatropous ovules pendent from the massive placenta at the 
stylar end. 
When ripe, the ovary wall consists of several layers of strongly cuticu- 
larized cells, the outermost of which grows out to form a thick investment 
of unicellular hairs. 
In some sections it is easy to observe mycelium in the fruit chambers, 
and about the enclosed seeds. Delicate branched hyphae are present in 
the cells of the wall, in the tissue of the central column, and in the funicles 
of the seeds. Branches from this mycelium grow across from the cells 
of the ovary wall to those of the seed-coat, and extend from one seed to 
another. 
The hyphae are septate, colourless, and so transparent in fixed 
material as to be visible with difficulty in balsam preparations unless 
stained. 
A microphotograph of a longitudinal section of such an unopened fruit 
is reproduced in PL VI, Fig. i a , and on this scale it is just possible to see 
the traversing hyphae. Parts of the same section, enlarged to show the 
details of infection, are shown in Fig. i b. 
The degree of infection apparent in seeds removed from unopened 
capsules is very variable. In some, a few hyphae project from the cells of 
the seed-coat; in others, mycelium is difficult to find, and can only be 
satisfactorily seen after the seeds have been specially treated; in others, 
hyphae are abundant all over the seed-coat. 
More especially is it difficult, as a rule, to observe hyphae on the testa 
of the resting seed, this difficulty of observation being due in part to the 
structure of the seed-coat. The latter is composed of a few cuticularized 
walls and an external layer of large cells which, during the final stages of 
development, break down, leaving at last only their ‘ foundations * (consisting 
of the inner walls and the proximal parts of the lateral walls) to form the 
regularly sculptured covering of the seed. The presence of the folded 
membranes of these cells, and of the remains of their contents, increases the 
difficulty of observing fine hyphae on the surface, after the seeds have 
become dry. 
According to Church, the seeds of Calluna are not shed until the 
following spring. ‘ The fruits ripen in late autumn (November), and the 
seeds are shed in the succeeding spring, when the capsules open under 
desiccation ’ ( 34 ). 
The behaviour of fruits in this respect doubtless varies with the 
locality and the season, but the observation does not appear to be of 
general application, since some difficulty has been experienced in finding 
unopened capsules after the middle of November. 
This, although a minor point, is worth recording, because it seems not 
