64 
M. Cheveley Rayner. 
From the earliest stages, whether growing in moist air or in soil, 
the roots are infected with an endotrophic mycorhiza. Branched 
hyphae project from the surface and many of the cortical cells 
contain the characteristic “knots” of mycelium. 
The plumule is undeveloped in the resting embryo and growth 
of the shoot is slow, especially in the early stages. 
In the “ heather” soil seedlings grow normally; the leaves are 
bright green and a vigorous much-branched root-system is rapidly 
formed (Plate III, Fig. la). 
Partial sterilization of this soil by carbon bisulphide, as 
described above (p. 62), gives an impetus to vegetative growth and 
the seedlings, for a time, compare favourably with the controls. 
Examined microscopically the roots of such seedlings are cleaner 
and fungal infection is rather less conspicuous (Plate III, Fig. lb). 
In the “chalk” soil, growth is practically inhibited. 
The few seedlings which germinate remain in the seed-leaf 
stage for many months. Sometimes no other leaves are formed : 
those which do appear are small and chlorotic, and the whole shoot 
usually becomes bright red in colour. Root growth is almost 
completely checked ; many lateral roots begin to develop, but their 
tips are strongly recurved and often show brownish discoloration 
(Plate III, Fig. lc). 
Seedlings may remain in this condition for months, making 
repeated but ineffectual efforts to form an adequate root system : if 
transplanted to the other soil, they at once recover and grow 
normally. Examined microscopically, these abnormal roots are 
remarkable, not only for the retarded growth and peculiar curvatures 
which they exhibit, but for the association with them of dense 
colonies of bacteria. The latter are especially conspicuous about 
the tips, which are usually invested with dense bacterial sheaths. 
Bacteria are also abundant in and about many of the cortical 
cells and around the apices of young emerging lateral roots 
(Plate III, Fig. 2b, Fig. 3). 
In “chalk” soil sterilized by either of the methods described 
on page 62 root development is more normal for a time. Bacterial 
growth appears to be retarded; a more normal root system is 
developed and reddening of the shoot takes place rather more 
slowly. This improvement, however, is temporary, and eventually 
the same symptoms appear as in roots in untreated soil (Plate III, 
Fig. Id). In all these abnormal roots, mycelium, though present, 
