194 TKANSACTIONS OF KOVAL SCOTTISH AKBOKICULTUKAL SOCIETY. 



greater in the plots free from living roots — usually two or three 

 times greater, and occasionally four and even six times. 



The results of these experiments clearly show that the 

 unsatisfactory condition of an undergrowth shaded laterally or 

 from above is not due altogether to insufficient light, but to 

 competition of the roots of the neighbouring old trees ; likewise 

 that the presence and condition of shrubs, grasses and mosses 

 in the forest depend very little upon the amount of light, but 

 are chiefly influenced by the degree of desiccation of the soil 

 caused by the roots of the old trees. Thus the poor development 

 of 3'oung growth directly under or near seed trees may be 

 explained, not by shading alone, nor by the mechanical action 

 of water dripping from the leaves and branches of the old trees, 

 nor by excessive light reflected from the trunks, but by the 

 moisture-sapping competition of the roots of the older trees 



In these experiments, however, Fricke, by eliminating com- 

 petition of the neighbouring roots, created artificial conditions 

 which do not exist in nature. Moreover, no photometric 

 measurements of any kind were made during these experiments,, 

 and without such measurements the question of light require- 

 ments of species cannot be settled. While the experiments 

 bring out the importance of considering other factors besides 

 light in the life of the forest, they do not prove that the light, 

 requirements of all species are the same. 



On fresh soils, with an abundant supply of moisture, root 

 competition affects the growth of the seedlings only a little or 

 not at all, and for this reason it is assumed that trees are more 

 tolerant on fresh or moist soils than on dry soils. But even on 

 the same kind of soil the effect of trees of different species upon 

 the growth of seedlings is not the same. Trees with a strongly 

 developed superficial-root system naturally desiccate the upper 

 layers of the soil much more than trees with a compact, deep- 

 root system. 



In filling blank places in plantations, the competition of the 

 roots determines the success or failure of the operation. It 

 happens only too often that the planting of blank places on dry 

 or only moderately fresh soils meets with entire failure, because 

 growth of the new seedlings is impossible in the dry soil 

 produced by the roots of the older seedling.s, which in the porous 

 soils of the planting holes attain extra good development. In 

 dry situations, therefore, blank places must be filled not later than 



