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species of trees. On the quite young stems, for instance, no bryophytic 

 growth is found. This is due, not to insufficiency of light in the young 

 plantations, but probably to the fact that the bark of very young trees 

 is so smooth as to offer no footing for such growth. As soon as the 

 trees have passed their first youth, small fissures are formed in the 

 periderm, and here the first Bryophyta make their appearance. These 

 are almost invariably acrocarpous: species of the genera Orlhotrichum 

 and Ulota. The growths occur in small isolated tufts, each attached 

 to the bark by a small surface only, radiating thence to all sides 

 without further connection with the stem. The pleurocarpous species 

 do not develop until later; these require in each case several distinct 

 points of attachment to the stem, which the sparsely fissured bark in 

 the early stages does not afford. With the bark in a more advanced 

 state of disintegration, however, they very soon appear, and owing to 

 their power of vegetative propagation, rapidly supplant the acrocarpous 

 mosses, finally covering the entire upper surface of the stem. 



In the case of very windy sites, the bryophytic vegetation will, 

 even on old trunks, be found to consist of Orthotrichum or Ulota species, 

 these being more xeromorphous in structure than those of the pleuro- 

 carpous group, which are unable to withstand the desiccating effect of 

 the wind. 



In the present investigations, Raunkiær's statistical method has 

 been employed (vide C. Raunkiær; Formationsundersøgelse og Forma- 

 tionsstatistik. Bot. Tidsskr. Bd. 30, 1908. Also, William Gr. Smith; Raun- 

 kiær's "life-forms" and statistical methods. The Journal of Ecology, Vol.1, 

 No. 1, March 1913). The result is shown in the tables. Each column 

 represents a locality, the figures indicating the degree of frequency for 

 each species, expressed in percentages. Only the upper (mossy) sides 

 of the stems have been investigated, and all stems dealt with stood 

 at an angle of more than 10°. The first line of the table gives the 

 diameter of the stem in cm; the second, degree of light in the planta- 

 tion in question (reckoned according to Wynne's actinometer, and ex- 

 pressed as a percentage of the daylight in the open). 



Tables 1, 2, 3 and 5 show the succession of the epiphytic Bryophyta 

 upon tree-trunks in Danish beech woods, the first column indicating 

 vegetation on the youngest stems, the last that of the oldest. 



Tables 6 and 8, the bryophytic growths and their succession on ash 

 stems (forest trees). 



Tables 9 and 10, bryophytic growths and their succession upon 

 oak stems (forest trees). 



Table 11, bryophytic growths and their succesion on alders (forest 

 trees). 



