38 Transactions British Mycological Society. 
single integument which is in the form of a characteristic net- 
work (Fig. 2) which varies somewhat in shape and structure in 
the different genera. On sectioning the seed (Fig. 3), or on 
viewing when stained and mounted whole, there is seen to be 
no differentiation into cotyledon, stem, radicle, as is almost 
universal in flowering plants*. It appears to be most usual for 
the cells at the suspensor end of the seed to be somewhat larger 
than at the upper end (Fig. 3), though this is not always the 
case (Cypripedium). Sometimes the suspensor cells are per- 
manent (Cattleya)—the suspensor is the stalk by which the 
developing seed is attached and nourished—at other times they 
disappear before the seed is matured (Phalaenopsis). Seeds 
taken from the capsule under sterile conditions and sown on 
ordinary substrata where no fungus is present do not as a rule 
develop. Generally they merely swell and become green (Odonto- 
glossum) though sometimes even this does not happen (Epiden- 
drum) ; in other cases they may form stomata and the rudiments 
of hairs (Cattleya). The only case so far known in which any 
considerable development can take place under these conditions 
is Bletilla hyacinthina where Bernard found that thin slender 
seedlings developed with distinct leaves. The food reserve of 
orchid seeds is most frequently oil, part of which becomes trans- 
formed into starch. The reserve food comes to its end just as 
the seed commences to become green. This is usually after three 
or four months, during which time very little, if any, nutriment 
can be obtained from the substratum, as absorbing hairs are 
lacking. If no fungus infection take place then, the seedling 
dies. It is somewhat surprising that after the production of 
chlorophyll death should occur rather than autonomous growth 
by aid of photosynthesis: the seedling appears to form chloro- 
phyll as a sort of last despairing effort. 
If, however, the appropriate fungus (i.e. the fungus from the 
root of the parent or some closely allied plant) be added now at 
the latest, an extraordinary change takes place. The fungus 
seems to give an impetus to development. 
In the culture flasks it is only in prearranged experiment that 
infection takes place at such a late stage. The fungus enters 
the seed usually within a few days. The course of events may 
be made out from the photomicrographs, which are taken from 
different genera in order to show the general similarity in the 
phenomena. Entry takes place at the suspensor end of the seed 
between the suspensor cells themselves, if such be retained. The 
cell walls here are unmodified, though the general surface of the 
* Bletilla hyacinthina shows a rudimentary cotyledon according to Bernard. 
Treub has indicated a cotyledon in Sobralia macrantha, and Pfitzer records 
a green embryo with a differentiated cotyledon in Platyclinis glumacea. 
