Germination of Forest Trees ir 
tion showed that the seed of Pinus monticola of Idaho lies in the 
duff and litter beneath the mature stands for years and then 
germinates when the ground is exposed to direct lighting. This 
is mentioned here, merely as another instance of the many of 
record in which it is assumed that light is to a large degree re- 
sponsible for the germination of certain tree seeds. 
Practically the only work of any importance on record concern- 
ing the effect of soil moisture and soil texture upon the early 
development of forest trees is that of Tolsky (8). He studied 
the relative effect of sandy and black soils upon the structure of 
the root system of Scotch pine. He found on black soils that 
pine developed principally vertical roots while on sandy soils 
superficial roots predominate. In rich soils roots are guided in 
their development by moisture, while in poor soils like sand, 
activity is directed mainly towards extracting nutrition from the 
soil. In poor soils nutrition is spread over a large area and in 
order to get it in sufficient quantities trees need numerous roots. 
Whatever the cause might be, Tolsky found more lateral roots 
and more superficial roots in the case of trees grown in sand, and 
this may be taken as the most significant part of his work. 
Before discussing the present investigations, I feel that it would 
be profitable to briefly summarize the edaphic factors of the 
habitat with special reference to the physical properties of the 
soil which play a physiological role in the germination of the 
seed, 
Classification and Résumé of Habitat Factors 
The complex of climatic, edaphic, and biotic factors which 
influences the life, growth, and reproduction of a plant is known 
as its habitat. The study and investigation of habitats as entities 
avails us very little unless we analyze a habitat into its component 
parts and investigate each of these parts by itself. 
Clements (1) classifies habitat factors into physical and biotic. 
The former have to do in general with inanimate objects and the 
latter with human beings and animals. He further divides phys- 
ical factors into climatic and edaphic. Climatic factors are atmos- 
pheric in their nature and the edaphic factors are concerned with 
