Rayner.—Obligate Symbiosis in Calluna vulgaris. 121 
independent existence ; from the moment of germination onwards it is 
a dual organism, the artificial synthesis of which has now been accomplished. 
The endosperm and embryo are the last strongholds of independence 
retained by the plant. 
It is interesting to speculate on the course of the evolutionary path 
which has been traversed, and to inquire if this condition of dependence 
has been reached as the result of a long series of capitulations on the part 
of the plant, each marking an extension of the area in which the Fungus is 
suffered as an endophyte in the tissues. 
When first extracted, the Fungus makes a rather weak growth on 
artificial media, but becomes more vigorous when subcultured. 
These differences in vigour are correlated with corresponding differences 
in the ease with which seedlings can be successfully inoculated. 
Thus, seedlings inoculated from a sub-culture growing on Calluna- 
extract gelatine immediately formed roots and continued to grow vigorously 
(PL VI, Fig. 14), while seedlings of the same age, inoculated from a strongly- 
growing old culture on rice, formed roots, but were at once partly or 
completely parasitized by the Fungus which became conspicuous externally 
on the leaves, or, in the case of weak seedlings, killed them outright before 
a root-system was formed (PI. VI, Fig. 16). 
In the former case the endophyte grew almost entirely below the 
surface of the rooting medium; in the latter it developed vigorously on 
the surface. 
Further investigations are in progress with regard to these differences 
of behaviour, which are evidently closely correlated with the nutritive 
conditions before and after infection. 
This was strikingly apparent in the two cultures from which repre¬ 
sentative seedlings are figured on PI. VI, Figs. 17, 18, and of which 
the history was as follows. Sterile seedlings were planted out on filter- 
paper in sterile tubes, inoculated from the vigorous rice culture mentioned 
above and supplied with distilled water, with the result that roots were 
formed in every case, although some of the seedlings showed signs of being 
too strongly invaded (PI. VI, Fig. 17). 
Seedlings similarly inoculated and planted out on paper, but supplied 
with a nutrient solution (Solution A (p. 106), 0-15 per cent, total concentration) 
instead of distilled water, were immediately attacked by the Fungus and 
destroyed, the mycelium subsequently forming an extremely vigorous growth 
on the paper (PI. VI, Fig. 18). 
The results of these isolation and inoculation experiments may be 
summarized as follows: 
i= A Fungus species, showing identical morphological characters in each 
case, has been isolated from the unopened fruit and from seeds removed 
from the unopened fruits of Calluna vulgaris . 
