8 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



(b) Lower canopy of trees which do not naturally attain to the 

 same height -birch, mountain ash, holly, field maple, aspen, 

 etc.; in the case of rejuvenating woods this lower canopy may 

 consist of the dominant trees in various stages of growth. 



{c) Upper layer of shrubs — hazel, elder, hawthorn, blackthorn, 

 etc. 



{d) Undershrubs or low woody plants which persist as under- 

 growth during winter — bramble and rose or ling and blaeberry. 



(<f) Tall herbaceous ground-vegetation of plants which dis- 

 appear almost entirely during winter — campion, dog's mercury, 

 bracken, male and other ferns. 



{/) Low herbaceous ground-vegetation — mosses, anemone, 

 celandine, wood sorrel, etc. 



The composition of the vegetation beneath the canopy depends 

 on several factors, especially variations in light and soil-moisture. 

 The plants are such as can bear some degree of shade, and all 

 plants which require full illumination are excluded and must 

 find their habitat away from trees. Amongst the herbaceous 

 plants of a wood there is a process of sorting-out. Some species 

 can live in deep shade, but the majority require at least a 

 moderate amount of light if they are to survive. The character 

 of the soil, wet or dry, light or heavy, leads also to variations 

 in distribution. During the life of a wood the conditions of 

 light and shade vary considerably from time to time. The 

 rank and tall herbaceous vegetation of a wood of young seedling 

 trees will in time become suppressed as the trees grow older and 

 the canopy becomes denser. When the canopy is densest and 

 shade is at a maximum the ground-vegetation will be at its 

 minimum. If the trees are thinned and more light is admitted, 

 the herbaceous and shrubby layers gradually increase, but so 

 long as trees remain the vegetation will be that of a wood. This 

 sequence of vegetation may be followed more readily in the case 

 of short period coppicing. When the coppice is tall, the dense 

 shade reduces the ground-vegetation and many of the plants 

 are unable to flower. Increased illumination on coppicing 

 enables the plants to recover, and in two or three seasons the 

 ground is covered with sheets of flowers. This brings us to the 

 important conclusion that although the vegetation of a wood 

 varies from time to time, and the abundance of species is liable 

 to considerable fluctuation, yet the number of species is fairly 

 constant. If this is so the ground - vegetation must be 



