DIRECT SOWING. 155 



be sown as soon as it ripens. In those regions of the 

 Himalayas, where snow may lie until late in the spring, both 

 autumn and sj)ring sowings are made, there being perhaps no 

 decided balance in favour of the one or the other season. 



r. Coverinfi Vie Seed. 



The objects of covering the seed are chiefly the following : — 



(1.) To protect it against sudden changes of moisture and 

 temperature. 



(2.) To protect it against being eaten by animals, especially 

 birds, or being carried away by wind or water. 



In natural woods large quantities of seed fall to the ground ; 

 some of it is carried by rain water through the vegetable 

 covering down to the mineral soil, thus finding conditions 

 favourable for germination. In artificial sowings the 

 necessary protection is afforded by covering it with earth 

 to a certain depth. 



The thickness of the covering is of considerable import- 

 ance ; if too thin, the seed is exposed to attacks by animals, 

 is liable to dry up or to be injured by frost ; if too thick, 

 germination is retarded, the seedlings have great difficulty 

 in pushing through the covering, and germination may 

 altogether fail for want of sufficient air. The actual thick- 

 ness depends on the general condition of the seed bed and 

 the species. It must be thicker in the case of loose or 

 dry soil, and thinner in firm or wet soil. 



The seed of different species requires a different covering. 

 On the whole, large seeds, such as acorns and chestnuts, 

 require the thickest covering ; considerably less, the seeds of 

 beech, maple, hornbeam, silver fir ; less again, those of alder, 

 ash, Scotch pine, spruce, and larch ; least, those of elm and 

 birch. 



According to experiments made by Baur* on loamy sand 



* Late Professor of Forestry at the University of Munich. 



