Orchid Mycorrhiza. J. Ramsbottom. 39 
seed is slightly cuticularized. As we have seen, the cells at the 
suspensor end of the seed are generally larger, and it is into 
these that the fungus passes (Figs. 3, 6, 7, 8). The cells are 
invaded by degrees, the hyphae becoming twisted into a ball 
in each cell before passing on to the next. Almost immediately 
the smaller cells at the opposite end of the seed undergo division. 
It is here that the meristem of the stem is laid down. The 
meristematic cells in orchids are never entered by the fungus: 
the only cells capable of division which ever harbour the endo- 
phyte appear to be those of the seed where it first enters. 
Eventually the developing seedling takes on a swollen shape 
most frequently more or less turbinate (Figs. 9, 10). 
Bernard uses the term ‘‘protocorm”’ for this swollen tubercle 
and regards it as of theoretical importance, as it simulates the 
protocorms of Lycopods and the colourless underground pro- 
thalli of Adder’s Tongues, etc. It is of interest to remark that 
a similar structure, also associated with fungi, occurs in the 
primitive fossil plant Hornea from the Devonian. The fungus 
remains restricted to the larger cells and follows in the wake 
of their division. The epidermal layer is free from infection. 
Meanwhile the rapid division taking place in the smaller cells 
at the anterior end of the seed gives rise to the young stem 
apex and the first leaf (cotyledon). About the time this young 
leaf becomes visible to the naked eye the cell-division has 
become extended along the axis and the beginning of the central 
stele is seen (Fig. 10). In this manner the young root is formed 
and begins to absorb its way through the tissues of the proto- 
corm (Fig. 11). Finally it passes out into the soil (Fig. 12). In 
no orchid studied in the present series (Odontoglossum, Oncidium, 
Cattleya, Cymbidium, Vanda, Cypripedium, etc.) does the de- 
veloping root when passing through the tissues enter the fungal 
zone nor do the hyphae extend into the root. In fact there is 
often a suggestion of a delimiting membrane separating the two 
areas (cf. Fig. 12). Thus when the root enters the soil it is 
absolutely free from infection; in none of the usually cultivated 
orchids does the root receive fungus from the swollen protocorm. 
Infection takes place from the soil most frequently when the root 
is about a quarter of an inch in length, the hyphae entering by 
the root hairs a little behind the region of greatest growth. This 
throwing off of the fungus, as it were, is repeated in orchids 
with tubers which do not retain their roots: the tuber is not 
infected and the new roots receive their fungus from the soil. 
In fact, in orchids so far studied it is only in the saprophytic 
Neottia that constant infection obtains. Here infection pro- 
gresses gradually from the widely infected protocorm into the 
body of the plant, gains the rhizome and infects the successive 
