112 



THE FACTORS [Part I 



hirsute form. Thus we have here a case parallel to that of the calciphilous 

 Gentiana acaulis and its calciphobous ally, Gentiana excisa. 



The choice of the substratum goes even further with many humus-plants, 

 especially among the lower cryptogams. Phanerogams and pteridophytes 

 are less exclusive, yet I always found Trichomanes sinuosum widely spread 

 in tropical America and growing exclusively on tree-ferns, and the North 

 American Epidendrum conopseum preferring the bark of magnolias to that 

 of other plants. 



Among mosses growing on humus, all intermediate forms are found 

 between those making a promiscuous choice of any kind of humus soil to 

 others showing quite a decided and often highly peculiar exclusiveness. 

 Decaying tree-stems have their characteristic species of mosses, such as 

 Plagiothecium silesiacum and Buxbaumia indusiata, which do not occur on 

 living trunks of trees. The latter have again a rich moss-flora (for instance 

 Leucodon sciuroides, many species of Orthotrichum), the components of 

 which do not appear in other habitats. Most epiphytic mosses are not 

 strict in their choice, although many are limited to definite kinds of trees. 

 Thus Orthotrichum leucomitrium occurs only on conifers, whilst species of 

 Zygodon, and Barbula latifolia, appear on broad-leaved trees only. More 

 strict in their selection are, for instance, Ulota Drummondii, which has been 

 obsei-ved only on Pyrus aucuparia ; Orthotrichum gymnostomum, which is 

 attached only to Populus tremula ; the rare Anacamptodon splachnoides, 

 which hitherto has been found only in cavities on the beech left by fallen 

 boughs. The Splachnaceae almost exclusively frequent animal humus.i 

 and are generally very strict in their choice ; thus Tayloria splachnoides| 

 occurs on decomposing bodies of several animals, and Tetraplodon mnioides 

 on various excrements ; Tayloria serrata, on the other hand, only on 

 decomposing human excrement, Tayloria Rudolphiana on the dung of 

 birds of prey as it lies on the boughs of trees, Tetraplodon urceolatus on 

 the dung of sheep, goats, and geese, Splachnum ampullaceum on cow-dung, 

 Splachnum luteum and S. rubrum on that of reindeer. 



Saprophytic fungi comport themselves like mosses. Many of them are 

 seen wherever the remains of plants and animals are decaying, others again 

 are confined to definite substrata. Thus species of Marasmius only occui 

 on fallen spruce needles, Antennatula pinophila only on fallen silver-fit 

 needles, Hypoderma Lauri only on fallen bay-leaves, Septoria Menyanthis 

 only on the submerged decomposing leaves of the buckbean, Poronia, 

 punctata only on cow-dung, Gymnoascus uncinatus only on decomposing 

 excrement of mice, Ctenomyces serratus only on rotting goose-feathers 

 Onygena corvina only on the down of birds of prey, Onygena equina only 



on rotting hoofs. 



