1922] RAYNER—NITROGEN FIXATION 233 
It had been observed previously that Calluna seedlings thrive only 
in solutions of extremely low total concentrations of salts (0.05 per 
cent). The experiments just described show further that in cul- 
tures of ‘‘synthetic’’ seedlings, the use of a culture fluid of 0.05 per 
cent total concentration affords optimum conditions for growth. 
The experiments have since been repeated, using every possible 
precaution to avoid contamination by traces of combined nitrogen. 
A similar solution of inorganic salts was made up in silica jelly 
prepared from specially purified materials and ammonia-free water. 
The cultures were planted in the autumn under unfavorable weather 
conditions, and seedlings did not root freely in the silica jelly, 
which seemed to offer mechanical difficulties. Otherwise, the 
results confirmed those already described. The seedlings deprived 
of combined nitrogen were green and healthy and grew at the same 
rate as the controls. 
It may be objected that seedlings of Calluna could grow for 
several months on the seed reserves, and that this accounts for 
the vigor and longevity shown by seedlings supplied with dis- 
tilled water only. Against this interpretation is the fact that 
seedlings germinated on moist filter paper from sterilized seeds 
not only form no roots, but make practically no shoot growth 
and quickly show symptoms of starvation such as yellowing and 
discoloration of the leaves. ‘These symptoms are relieved by inocu- 
lation from a pure culture of the endophyte. Finally, there can 
be no doubt that the optimum conditions in artificial cultures for 
the establishment and maintenance of a properly balanced relation 
between plant and endophyte are supplied by a rooting medium o 
extremely low concentration of salts (for example, 0.05 per cent) 
lacking combined nitrogen. A fresh line of research is hereby sug- 
gested in order to ascertain whether the unfavorable symptoms 
shown by seedlings planted in culture solutions of higher concentra- 
tion of salts can be specially correlated with the supply of nitrates. 
It is certain that a very small alteration in the character of the 
nutrient supplied to “synthetic” seedlings overthrows the normal 
balance and induces parasitism in the endophyte. 
(3) ADDITIONAL EVIDENCE ON NITROGEN FIXATION IN PHOMA.— 
An indirect contribution to the subject has recently been made by 
