32 Transactions British Mycological Society. 
orchids so far investigated possess mycorrhiza, with the single 
exception of the saprophytic Wullschlaegelia aphylla*. Large 
numbers both of native and exotic species have been studied— 
Wahrlicht+, for example, examined over 500 of the latter culti- 
vated at Moscow. 
Since the earliest workers, e.g. Reissek, it has been known that 
in some cells at least the fungus becomes changed from its original 
thread-like structure into glary yellow amorphous masses. In 
fact, it was owing to this phenomenon that the fungal nature 
of the cell infections of these roots was not at first generally 
realised. Wahrlich paid special attention to the changes which 
took place, and most investigators of orchid roots since then 
have taken note of them. Magnust working with Neottza in 
which the alterations are well marked gave a clear description 
of the metamorphosis. He distinguished two main types of 
infected cells and held that there were no transitional stages. 
In the one type which he calls “digesting cells’’ (Verdauungs- 
zellen) the fungus always degenerates; in the other type, the 
“host cells” (Pilzwirthszellen) the fungus remains alive in the 
cells which lodge it and is thus able to hibernate. Magnus states 
that Neottia shows a more or less definite arrangement of these 
two types of cells, the digesting cells forming an outer and an 
inner and the host cells the middle layer. Such a regular 
arrangement isnot usual in orchids—even in Neottia it is doubtful 
—and host cells are absent in certain native genera, such as 
Goodyera, and in most tropical forms. Bernard and Burgeff have 
also studied the question of the fungus digestion—the former 
mainly in seedlings, the latter principally in the root of Platan- 
thera chlorantha. Before a hypha enters a host cell the nucleus 
of the latter increases in size. This action at a distance is also 
seen in the fact that starch disappears from the cells. The 
nucleus in the neighbourhood of the hypha becomes hyper- 
trophied, often becomes modified in form and has increased 
attraction for stains. Where mycelial influence is great the 
nucleus becomes amoeboid and sometimes disintegrates: this 
would seem to indicate a parasitic action on the part of the 
fungus. The digesting cells are clearly recognisable by the de- 
generating mass which more than half fills the cells. The increase 
in the size of the nucleus is also a character as it becomes about 
four times its original diameter, i.e. roughly sixty times the 
* Further investigation is needed on this plant. MacDougal first recorded 
that Cephalantheragoregana was free from fungus, but later found a somewhat 
sparse and intermittent infection. 
+ W. K. Wahrlich, Beitrage zur Kenntnis der Orchideenwurzelpilze. Bot. 
Zeit. XLIV, pp. 481, 497 (1886). 
+ W. Magnus, Studien an der endotrophen Mycorrhiza von Neottia Nidus- 
avis L. Jahr. f. wissensch. Bot. xxxv, pp. 205-272 (1800). 
“ 
