402 Salisbury . — The Soils of Blakeney Point : A Study of Soil 
mainly responsible for the water capacity of dune soils , and it is in conformity 
with this that the roots of ephemerals (cf. Text-fig. 2) tend to occupy the 
upper layers of the soil in which the humus is mainly present. Also it is 
significant that numerous rootlets are often developed around old buried 
rabbit droppings with which the root systems may come in contact. 
Text-fig. 2. Root systems of Cerastium semidecandrum , Phleum arenarium , and Draba 
verna , three dune ephemerals, showing their shallow character. (§ natural size.) 
The subject of the nature and extent of root systems cannot be gone 
into here, but it may be mentioned that careful study of those of several 
ephemeral species shows that the volume of soil exploited is about 360 c.c. 
in Cerastium semidecandrum , 160— 430 c.c. in Phleum arenarium , 75 ° c * c * * n 
MyoSotis collina . In most cases the average depth of the root systems 
of the ephemerals is about 12 cm. 
In contrast to this, the larger plants have very extensive and deep 
