168 M. Chevely Rayner. 
unique among Flowering plants. The root-fungus of Calluua not 
only forms mycorhiza hut extends throughout the plant in an 
extremely attenuated condition into the tissues of the shoot and 
leaves. In turn the ovary of the flower becomes infected and 
hyphae grow across from the wall to the seed-coats of the young 
seeds within the ovary chambers. When these are ripened and 
shed they carry with them their fungal partner in the form of 
delicate hyphae on the surface of the seed-coat. Conditions 
responsible for the awakening to growth of the plant embryo at 
germination favour a corresponding activity in the mycelium, which 
infects the young seedling and determines in this way its further 
development. 
Doubtless the low germination capacity and irregular germin¬ 
ation observable in ericaceous seeds may be attributed—as in the 
orchids—to failure of the fungus to ‘ make good ’ at a critical stage, 
perhaps sometimes to death of the seed-coat mycelium from 
desiccation. 
As compared with the orchids, the problem of infection in 
Ericaceae has been solved in a different way. ^Infection is more 
certain, but the plant takes the increased risk inseparable from the 
presence of a facultative parasite in the assimilating tissues. In 
this case also there is immunity , determined, as in the orchids, by 
the power of the plant-cell to hold the invader in check. 
The extensive researches of Gallaud (15) on mycorhiza are worthy 
of notice. They were undertaken to investigate cases in which the 
relations between plant and fungus are simpler and presumably 
more primitive than in the orchids. The author describes in detail 
numerous cases of mycorhiza selected from different groups of 
plants, many of which were previously unrecorded. He discusses 
certain morphological structures in the endophyte and their 
functions, and gives a general critical survey of the. state of 
knowledge at the time when the papers were written. 
Gallaud’s original observations may be summarized as follows:— 
The habit of forming endophytic mycorhiza is common and 
widely distributed in both Monocotyledons and Dicotyledons and 
occurs in plants belonging to widely separated families. 
Infection of the roots is constant for many species, inconstant 
for others and shows morphological characters which permit of 
classification into groups. 
None of the fungi concerned was successfully isolated by 
Gallaud. When growing as endophytes spores are not formed and 
their systematic position therefore remains doubtful. 
