Orchid Mycorrhiza. J. Ramsbottom. 49 
the epidermal cells: they show no preference for special points 
of entrance or egress, penetrating with equal ease the cuticu- 
larized cells of the epidermis or the base of a hair. The ovary— 
and later the young fruit—contains mycelium in all parts of the 
internal tissues. This mycelium infects the seed coats of the 
developing seeds. The embryo and endosperm of the resting 
seed are free from infection. 
Thus, as in Neottia, we are dealing, except in the seed, with 
a dual organism. The type of association is, however, different 
from what obtains in the orchids so far studied, where no such 
distribution has been found—and an analogous constancy ap- 
parently only occurs in non-chlorophyllous genera. From the 
fact that Rayner has recorded the presence of ovarial infection 
in a number of Ericaceae—Rhododendroideae, Arbutoideae, 
Vaccinioideae and Ericoideae—it may be that the fungus is 
similarly distributed throughout the tissues of these plants, and 
presumably obligate symbiosis is to be inferred. 
In no other case has the necessity of the presence of the 
mycorrhizal fungus for germination been proved. There can be 
hardly any doubt, however, that such a phenomenon is not 
restricted to two groups so widely separated as the Orchidaceae 
and the Ericaceae. What have these families in common? 
Apart from the similarity in habitat of certain species there 
seems to be nothing except the smallness of their seeds—and it 
is naturally to seed characters that one looks in this connection. 
As we have seen, the seeds of orchids are exceedingly small; 
reduction in most genera would appear to have reached its limit. 
In typical Ericaceae the seed is very small, rarely exceeding 
2mm. and often less than half this size. There is a richly de- 
veloped endosperm in which a straight embryo is embedded 
one-half to two-thirds the length of the seed, always showing 
a root, an axis and two cotyledons more or less differentiated. 
It is also of interest to remark that such genera as Kalmia and 
Ledum have a net-work integument to the seed. 
PYROLACEAE. 
Allied to the Ericaceae is the family Pyrolaceae with the 
sub-families Pyroloideae and Monotropoideae. In families of 
flowering plants which show saprophytism and parasitism there 
usually occur green purely autophytic plants, with typical green 
leaves and numerous flowers; plants that are purely saprophytic 
or parasitic, with colourless scales and a reduced number of 
flowers; and all gradations between. Henderson* instances the 
* M. W. Henderson, A comparative study of the structure and saprophytism 
of the Pyrolaceae and Monotropaceae with reference to their derivation from 
the Ericaceae, Contrib. Bot. Lab. Univ. Pennsylvania, v, pp. 42-109 (1919). 
M.S, 4 
