226 ELEMENTS OF SYLVICULTUEE. 



by causing the soil to expand, compels them to fol- 

 low the upward movement, and when thaw sets in, 

 the young plants run the danger of having their roots 

 laid bare. It cannot therefore be laid down as an in- 

 variable dictum that autumn is preferable to spring 

 or vice versa. The question is entirely one of local 

 conditions. Besides, this choice does not always exist, 

 and if large areas are to be planted up, there is no 

 alternative but to distribute the work between the 

 two seasons. The essential thing is to plant carefully. 



To that end the forester must first occupy himself 

 with pit-making, the interval to be left between the 

 pits, the pruning of the seedlings, and putting 

 them into the ground. In the second place, he 

 must examine the different methods of planting. 



The pits ought to be deep enough to enable the 

 plants, with all their roots, to be put into the ground 

 in perfect freedom, and as low down as they were 

 before. As for tall seedlings, for which large holes 

 are of course necessary, it is an advantage to separate 

 the different layers of soil, so that the best may be 

 put in immediate contact with the roots. But what- 

 ever the class of plants used, it is always better to 

 prepare the pits before they are wanted, in order to 

 loosen the soil and subject it to the action of the 

 atmosphere. Moreover, the work is done more 



* Three primcipal results follow from exposure to the air, of which 

 two are chemical and the third physical. They are as follows : 



1. Formation of ammonia, and of nitrous and nitric acid, known 

 technically as nitrification of the soil. 



2. Transformation of insoluble into soluble substances ; thus carbonate 

 of lime which is insoluble is changed into bicarbonate of lime which is 

 soluble, the decomposition of vegetable detritus is facilitated, &c. 



3. (Partly a consequence of 2.) The cohesion of the soil is diminished . 



