THE ORCHID REVIEW. 103 



accumulations of decaying vegetable matter, regardless of situation if the 

 other conditions are favourable. As time goes on particles of inorganic 

 dust collect in the forks of the branches and rents and fissures of the bark 

 of old trees, and these get mixed with fallen leaves and twigs and particles 

 of crumbled bark, forming a vegetable mould which is an excellent soil 

 for a large number of plants. So much is this the case that plants which 

 are normally terrestrial are often found in such situations. It has been well 

 said that Nature has very few unoccupied places, and these plants have 

 < stablished themselves there because the conditions are favourable. 



The plants which we are particularly speaking of are largely tropical 

 and sub-tropical. In cold regions the plants that grow in the mould of the 

 bark are for the most part mosses, liverworts and lichens, but in the tropics 

 such situations form the rallying ground for a host of ferns and flowering 

 plants. Small ferns are so numerous as to wreath the trunks, and with these 

 are found Aroidese, Orchids, Bromeliads, &c. It has been remarked that 

 the Bromeliads chiefly ornament the forks of the trunks, while Orchids, 

 Dorstenieae and the various species of Rhipsalis grow on the upper surfaces 

 of branches that ramify horizontally, while Aroideae and Begonias take 

 root for the most part on the surfaces of high erect trunks. 



The bark itself, that is the cortical layer, dead, but not yet crumbled 

 and mouldered into dust, forms a nutrient substratum for a series of plants 

 of various affinity — lichens, fungi, mosses, and higher plants. Even in the 

 case of tropical Orchids growing on a substratum of bark, if the roots are 

 forcibly detached, little fragments of the bark will be found torn off with 

 the rhizoids at the places where they issue from the stems. The majority 

 no doubt nestle in the mould-filled crevices in the bark, and nourish them- 

 selves, besides, by means of special aerial roots which hang down in white 

 ropes and threads, like a mane, from the places where the plants are 

 situated. Some of these roots are flattened, and adhere firmly to the bark 

 with their flat surfaces, like the roots of Phalaenopsis Schilleriana, and on 

 the under surface, behind the growing point, is a whitish fur, consisting of 

 short, thickly packed, absorptive cells, and these adhere so tightly that 

 i t is often easier to detach small pieces of the bark than the root itself. 

 Similar conditions have been observed in the roots of many other epiphytes. 

 A curious fact has been observed in connection with these plants, namely, 

 that when transferred to loose earth, devoid of humus, they languish, 

 because Iheir roots are unable to enter into union with a support of such 

 loose texture, and this is true of most tropical Orchids that live upon bark. 

 It has also been observed that the seeds of such Orchids do not germinate 

 on a loose substratum, but when on the bark of a tree they germinate, and 

 develop into healthy plants. 



When steep rocks occur near clumps of trees it is not uncommon for the 



