The Ecology of Calluna vulgaris. 65 
is scanty in amount, few hyphae project from the root and they are 
often crowded with bacteria. 
The effect of watering seedlings growing in “heather” soil 
with a watery extract of “chalk” soil has been tried, with the 
following results :— 
After four months of regular treatment seedlings in small pots 
do not differ markedly from the controls. After six to seven 
months treatment, seven out of eight seedlings so treated begin to 
show signs of injury. Growth was stunted, the foliage yellowish 
and discoloured, and the leaves dead on some of the older shoots 
(Plate III, Fig 4). 
Examined microscopically, the roots of these seedlings show in 
a rather less marked degree the same peculiarities as have been 
already described for roots growing in “ chalk ” soil. Root growth 
is evidently checked, the tips show marked curvatures and are 
often invested with a dense mantle of bacteria. Mycorhizal growth 
is poorly developed and the general appearance of the roots quite 
characteristic. 
Seedlings growing in larger pots responded to similar treatment 
much more slowly. After treatment for the same length of time, 
the growth and general condition of the shoot was practically 
unaffected. 
Many of the root-tips, however, when examined microscopically, 
showed characteristic association of the mycelium with bacteria, 
the relations of the hyphae with the latter being much more evident 
in such early stages than they are later when the tip has become 
invested in a dense sheath of bacterial growth. 
Other seedlings growing in “ chalk” soil were watered with an 
extract of “heather” soil prepared similarly to that used in the 
last experiment. This experiment was begun shortly after germin¬ 
ation, before the ill effects of the unfavourable soil conditions had 
become marked, and was continued for six months. At the end of 
that period the controls—watered with distilled water—were dead ; 
the seedlings in the three pots under treatment were alive ; the 
characteristic purpling of the leaves had appeared, but most of the 
plants had made four to six leaves on the main axis. 
The change in the root system was more remarkable and is 
shown in Plate III, Fig. 5. 
As is evident from a comparison of this photograph with that 
of the seedlings shown in Plate III, Fig. lc, the root system is 
many times larger than that of a seedling from untreated soil. 
