62 
M. Cheveley Rayner. 
The phenomenon of retarded germination in a soil unfavourable 
to the growth of the plant does not appear, therefore, to be one 
which occurs generally in the case of calcicole and calcifuge plants. 
Heating Calluna seed for some hours at a temperature of 67 n C. 
to 70 n C. hastens germination, the acceleration so produced being 
more marked in the autumn. 
Seed so treated germinates more evenly and about seven days 
sooner than unheated seed. 
Heating for a longer period, e.g., twenty hours at 70°C. affects 
the germination capacity adversely, but not the vitality or rate of 
germination of those seeds which germinate. 
No difference can be detected in the behaviour of seeds 
germinated at once after heating and those kept for several weeks 
before sowing. 
Partial sterilization of the soil, by treatment with vapour of 
carbon bisulphide and by heat, gives somewhat irregular germin¬ 
ation results, which are summarized in Table I. The soil for these 
experiments was treated as follows: — 
Small quantities of soil were spread out in carbon bisulphide 
vapour for three or four days, then exposed freely to the air for 
several days, placed in small sterile pots and watered with distilled 
water, Other samples of soil were subjected to intermittent 
heating at 92"C. and 98°C. on five successive days, moistening with 
sterile water between each heating. The seed used for these 
experiments was in all cases untreated, and control seeds of oat 
placed in the pots germinated normally. 
Reference to the tabulated records shows that the behaviour 
of the seedlings when the unfavourable soil is subjected to partial 
sterilization is noteworthy and in striking contrast with their 
reaction to the same soil untreated. The germination capacity 
remains low as in untreated soil, but the rate of germination is 
accelerated. The resulting seedlings develop a larger and more 
normal root system (Plate III, Fig. Id). 
B. Growth. Seedlings of Calluna are small and slow-growing 
The primary root elongates slowly, but soon after germination 
several adventitious roots grow out in rapid succession from a 
thickening at the base of the hypocotyl. 
The roots are almost transparent and provide beautiful material 
for observing the details of root structure. Root hairs are absent; 
the cortex consists of a few cell rows only, and the whole root is 
extremely slender and delicate. 
