84 Richard H. Boerker 
merely the luminous energy or the heat energy of the sun or both 
is difficult to say. Asa general thing it is impossible to have light 
energy without a certain amount of heat energy, but heat and 
light affect plants so differently that the final effect of these 
factors is easily recognized. It is important to keep these two 
concepts separate in order to avoid confusion. Graves also makes 
the statement that light is necessary for the germination of 
Western White pine. ~ It is inconceivable how luminous energy 
can play any part in germination, especially when the seeds are 
below the ground; it is likewise difficult to conceive what possible 
effect light could have if it did reach the seed. 
7. An inadequate supply of soil moisture delays germination. 
8. An inadequate supply of soil moisture decreases the length 
of the germination period. 
g. A lack of soil moisture decreases the final germination per 
cent. 
10. The germination curves of seeds sown in wet soil rises 
much more rapidly than that of seeds sown in dry soil. 
I1. Xerophilous species begin germination first, xero-meso- 
philous germinate Jater, and mesophilous germinate Jast. 
12. ‘The germination period of xerophilous species is shorter 
than that for either the xero-mesophilous or the mesophilous 
species. 
13. In xerophilous species germination is accelerated in the 
gravel and sand; in mesophilous species it is accelerated in loam 
and sand. In general germination is accelerated in sand and 
gravel due not to the amount of soil moisture in these soils (see 
accompanying diagram) but to the amount of oxygen in the soil. 
14. The germination period is longest in the sand. 
15. The germination per cent. is usually highest in the sand. 
16. The rise of the germination curve of seeds sown in sand 
is usually more rapid than of seeds sown in loam or gravel. 
17. According to the table on page 29 of this report the volume 
of air space in a given volume of soil is about 39 per cent. for 
gravel, 33..per cent. for sand, and 53 per cent. tor loam. Ingthe 
accompanying diagram is shown the amount of capillary water in 
these soils at the time of watering and twenty-four hours later. 
