INFLUENCE OF VEGETAL LIFE. 301 



selves. This direct solvent action of roots and rootlets upon rocks has 

 been practically demonstrated by Sachs.* 



IV. But, however important these operations may be, it is to the last 

 agency — the formation of acids by decay — that attention is especially 

 directed. 



The richness — rankness — of Brazilian vegetation, except, of course, in 

 the campo region, is almost incredible. If a forest be cleared away and 

 then left to itself it grows up so quickly that in three or four years it 

 looks almost like a primeval forest, except in the cases of a few of the 

 slower growing trees, such as rosewoods, hraunas and perohas. The forests 

 of the forest regions are literally impenetrable except by the use of the 

 facdo or big forest knife. Where they are traversed by roads one can 

 often travel for days in a twilight gloom without getting more than occa- 

 sional glimpses of the sky. 



" Plus on avance dans ces forets, et moins il y a d'ouvertures : on peat y marcher 

 I'espace de plusieurs jours, et le ciel se montre rarement a travers les routes aeri- 

 ennes dont la verdure recouvre le voyageur." f 



Mr Clark gives the following graphic description of the forests of the 

 Organ mountains : J 



" We were in the deepest shade ; some 50 or 80 feet above our heads were the 

 bushy tops of closely packed trees ; then below them a second covering of palms, 

 fern trees, and such like, all loaded with parasites ; below them again was thick- 

 tangled brushwood, not in the least like our English brushwood, that good naturedly 

 gives way to your arms and hands as you stride through it, but interlaced in all di- 

 rections with long trailing, creeping plants, some with stems as thick as my wrist, 

 others thinner ; the thinnest and by far the worst for us were thread-like runners 

 that were no thicker than string, so tough that to break them was impossible and 

 so long that they would not give way before us. Underneath this monster vege- 

 table net . . . was the ground, covered with masses of dead leaves, broken 

 branches, all the debris of the vast vegetable creation above that had been accumu- 

 lating for countless ages, and often green with little plants and ferns." 



The darkness of these forests, however, is seldom a cool shade ; the 

 hot air is reeking with moisture and the conditions highly favorable for 

 plant growth. But while vegetable growth is notoriously rapid and rank 

 its decay is equally rapid, and this decay produces large quantities of 

 organic acids, which are carried by the rains into the soil and the under- 

 lying rocks. Even on the barest rock surfaces there is always consider- 

 able vegetation in the form of lichens, liverworts and small epiphytes 

 (bromelias). These plants furnish but little protection against the me- 

 chanical wearing of the rocks, while they contribute destructive acids to 



♦ Experimental Physiologie, p. 188 ; Johnson's How Crops Feed, p. 326; Bot. Zeitung, 1860, p. 118. 



t Voyage Pittoresque dans le Bresil. Maurice Rugendas. Paris, 1835, p. 10, 



I Letters Home from Spain, Algeria and Brazil. Hamlet Clark;. London, 1867, p. 123. 



