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Tables 12 and 13, bryophytic growths and their succession on elms 

 (of which 12 forest trees and 13 situate on open ground). 



Table 14, bryophytic growths on Acer pseudoplatanus (forest trees). 



Table 15, bryophytic growths on Populus virginiana (open ground). 



The species of trees here investigated may be divided into two 

 groups, comprising 1. the smooth-barked species, and 2. those with 

 scabrous bark. Each of these two groups has its own peculiar bryophytic 

 vegetation, differing from that of the other; within each group, however, 

 only slight differences exist. 



The ash and the beech, both smooth-barked species, exhibit, it is 

 true, an apparently considerable difference in their epiphytic vegetation; 

 this dissimilarity is, however, mainly due to the difference in power of 

 light absorption between the two species. A beech tree for instance, 

 growing in a strong light (e. g. on the fringe of a wood) will exhibit 

 very much the same epiphytic vegetation as found on the stems of 

 the ash. 



The epiphytic Bryophyta communities are xerophilous. The following 

 xeromorphous characters are found: 

 Thick cell membranes (Fig. 2). 

 Papillæ on leaves (Fig. 2). 



Leaves can in dry weather close in towards the stem (Fig. 3 shows 

 Orthotrichum Lyelli — on Fraxinus — in damp weather, and Fig. 4 the 

 same growth in dry). 



High degree of osmotic pressure in the cells (Table 16). 



Some species can press close in upon the bark. 



Only a few epiphytic Bryophyta are photophilous {Orthotrichum 

 species); most of them can endure a high degree of shade. This is 

 especially the case with Hypnum cupressiforme, which has a light mini- 

 mum equal to less than 0.4 °/o of daylight in the open. 



As regards the chemical composition of the soil, the abundance 

 or paucity of chalk appears to exert a certain influence here. Antitrichia 

 curtipendula and Frullania Tamarisci are only found in woods where 

 the soil is sandy and contains but little chalk (Tab. 3, 4, 5 and 10), 

 while in the forest areas of the moraine clay, where chalk is more 

 abundant (Tab. 1 and 9), these two species are either altogether lacking 

 or but sparsely found. They should therefore be described as calcifugal. 



