178 FORMATIONS AND GUILDS [Part I 



iii. OPEN EDAPHIC FORMATIONS. 



In many places the physical texture of the soil is such that it doe: 

 not permit the existence of closed formations. A feature that in desert 

 is due to climate, in this case is due to the nature of the soil. Th. 

 soil is occupied by those plants that are able to establish themselve 

 on it in spite of the unfavourable conditions. There are but few- 

 such plants, however, and the formation remains open throughout, si 

 that there is still space left for many plants, and accordingl}' there is n^ 

 struggle between competitors. Whatever the climate may be, sucl 

 places possess the character neither of woodland nor of grassland, bu 

 produce a confused mixture of woody and herbaceous plants that ar 

 quite independent of one another. 



To the open formations of the kind just described belong, in the firs 

 place, those of rock-plants. Naked rock, after cooling down from 

 molten condition, or after separation from a larger mass of rod 

 remains bare of vegetation for a longer or shorter period. Sooner c 

 later, sooner in a damp climate than in a dry one, plants appear on if 

 surface, at first small Algae and lichens later on, and after these mo: 

 accommodating plants have produced a little humus, mosses and highf 

 plants. The vegetation on the surface of rocks or stones may be terme 

 that of litlwpJiytes. Crevices in rocks, in which more finely graine 

 components and more water accumulate than on the surface, produc 

 a somewhat more copious vegetation, that of the cJiasviopliylcs. 

 formation of plants on rock consists either of lithophj'tes only, especial! 

 if the rock is free from cracks, or of lithophytes and chasmophytes. 



Lithoph\'tes are low, flat, spreading plants, the superficial developmei 

 of which is sometimes determined chiefly by the roots, sometimes by tl 

 shoots, which by the help of small roots — or in thallophytes b}' rhizoic 

 • — become attached to the hard substratum. Mosses and phanerogan 

 frequently assume the form of cushions. Chasmophytes, as opposed 

 lithophytes, are long straggling plants, since their substratum often 11 

 at the bottom of a crevice at a great distance from its mouth ai 

 therefore from the light. Hence, many chasmophytes possess extreme 

 long rhizomes and roots, yet such extreme forms are less frequent 

 rocky crevices than among gravels, which owe their origin to the di 

 integration of rocks under the influence of atmospheric agencies, and whii 

 usually form large heaps at the foot of the masses of rock from whi' 

 they have fallen, or create the moraines along the course of glacic 

 On these gravels lithophytes are much less frequent than chasmophyti 

 and the chasmophytes exhibit the frequently extraordinary growth 

 length to which reference has just been made. 



Some of the fragments of rock come down to the water-coursi 



