94 



BULLETIN 1105, U. S. DEPARTMENT OF AGRICULTURE. 



suits as shown in Table 21. From this it is evident that if the brush 

 was beneficial it was not sufficiently so to aid reproduction in a 

 measurable degree. 



Table 21. — Effect of brush on germination and survival of seedlings, cinder area. 



Date of examination. 



Number 

 of plots. 



Total 

 area. 



Number of seed- 

 lings per acre. 1 



Brush. No brush, 



Remarks. 



1909. Aug. 19 



Sept. 22 



Nov. 19 



1910. Sept. 13 



1911. Sept. 9 



1912. July 



1913 



1920. August. 



1919. General, both 

 brush and no brush. 



Sq.fcd. 

 500 

 500 

 500 

 500 

 5,000 

 1,000 



Acres. 

 1.2 

 1.5 



13,100 



7,800 



1,950 



218 



35 



87 



19' 9m ll909-10 counts all on the same plots: 

 6 100 'I aU seedlin S s of 1909 germination. 

 2^395 



87 

 174 



82 per cent of "no brush" on 1 plot. 

 All seedlings of 1909 germination. 

 New plots; includes some of 1911 germ- 

 ination. 



Includes a few originating after 1909. 

 Ages 4 to 10 years: all germinated 1909 



or later. 

 Ages, 4 to 20 years. 



1 1909 and 1910 records are for identical plots. After 1910 new plots were selected for each examination. 



Physical conditions. — In conjunction with the seedling records, 

 experiments were conducted with the object of determining in a 

 quantitative way the effect of a brush cover upon physical conditions 

 which were thought to have an important influence upon*Seedling 

 growth. Some of these effects are so obvious as to require no experi- 

 mental proof. For example, it is known from observation that brush 

 cuts off the light to such an extent as to endanger the life of seedlings 

 beneath it. Other effects, such as smothering, are equally obvious. 

 Certain other anticipated effects are less easily demonstrated. It is 

 reasonable to suppose that seedlings situated so as to be only partially 

 screened may be benefited by reduction of excessive transpiration, 

 protection against wind and frost, and conservation of soil moisture 

 without suffering the injurious effects of too much cover. In the 

 fall of 1908 thermometers placed under a cover of green branches 

 at night showed temperatures from 1° to 5° F. higher than those a 

 few feet from the brush. During the same year unprotected first- 

 year seedlings were killed by an early freeze, while on a plot covered 

 by brush they were uninjured. Even a light screen reduces tran- 

 spiration; but no experiments have been conducted to prove how 

 effective a light brush cover may be. 



Soil moisture. — Most of the experimental work has centered on 

 the question of soil moisture. How effective is a brush cover against 

 loss of soil moisture? The results of samplings in 1909 and 1912 

 are given in Table 22 and Figure 12. Xo determinations of wilting 

 coefficient were made at the time these samples were taken. Deter- 

 minations in 1920 for samples secured in the immediate vicinity of 



