I'KRIODICAL LITERATURE ^29 



aeration. The intervening spaces between the soil particles is occupied 

 by water and air, the water being found in thin films around the soil 

 particles while the air fills the remainder of the pore space. Since the 

 air is being called on to provide a constant supply of oxygen for respi- 

 ration and in turn receives fresh supplies of carbon dioxide, efficient 

 ventilation is very essential if the air in the pore spaces is to remian 

 fresh. There must be a diffusion of gases between the soil and the 

 atmosphere above; supplies of oxygen must pass into the soil and at 

 the same time the excess carbon dioxide passes to the atmosphere. 

 Three gases are involved — oxygen, carbon dioxide, and nitrogen. In 

 general the oxygen and carbon dioxide contents are reciprocal — the 

 amount of oxygen in the soil decreasing as the amount of carbon 

 dioxide increases and vice versa. The water films were found generally 

 to be very poor in oxygen but very rich in carbon dioxide. Rain, which 

 was found in most cases to be a saturated solution of oxygen, resulted 

 in a marked stimulation of the biological activities of the soil. 



Because of the difficulty encountered in establishing a vigorous 

 growth of Sal (Shorea robusta) seedlings, a study of the factors 

 influencing germination and development of seedlings was undertaken 

 at the Forest Research Institute at Dehra Dun in 1909. Pot experi- 

 ments showed that while it was practically impossible to injure Sal seed 

 and seedlings by watering in sand, germination could be materially 

 reduced and the seedlings rapidly rendered unhealthy in water-retain- 

 ing loam and leaf-mould by keeping the soil constantly moist. Similar 

 results were subsequently obtained with loam taken from a local Sal 

 forest. The injurious action was most severe in the leaf mould which 

 contained considerably more organic matter than the loam. 



Simultaneously with these pot experiments, a series of experiments 

 was conducted in the Dehra Dun Sal forests. These showed that, while 

 in^the shade of the forest germination and seedling development during 

 the rainy season was uniformly poor, even when the soil covering of 

 dead leaves is removed and the soil dug up, excellent seedling growth 

 can be obtained if the trees are felled in narrow strips or small patches 

 and the seed then sown in the clearings where the soil is exposed to 

 the sun and air. It was clearly demonstrated that the injurious agent 

 was a soil factor and not deficient light by growing healthy seedlings 

 with well-developed roots in pots containing sand placed in the shade 

 of the forest. Many of the seedlings appeared quite healthy with 

 green leaves above ground while a number of the deeper roots were 



