84 Richard H. Boerker 



merely the luminous energy or the heat energy of the sun or both 

 is difficult to say. As a 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. 



9. 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. 



11. Xerophilous species begin germination first, xero-meso- 

 philous germinate later, and mesophilous germinate last. 



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, for loam. In the 

 accompanying diagram is shown the amount of capillary water in 

 these soils at the time of watering and twenty-four hours later. 



