( ^3 ) 



If we may rely upon Eev. Ch. Parish's " Botanical Notes, made during a month's tour 

 from Moulmein to the three pagodas, &c,"* the part which lime and silica play would 

 appear to be not very important in Burmah. Unfortunately, I myself have never had an 

 opportunity to explore pure limestone districts in India, and this circumstance has been a 

 great drawback in all my studies regarding the influence of chemical composition upon 

 vegetation in India. 



In the above notes it is indicated that chemical influence exists, and that it is of primary 

 importance. I may now show that the physical structure of rocks, &c., is not less important. 



It is all very well to shew from an analysis, that all chemical constituents are present, 

 and in the needful proportions ; but a more important question, it would seem to me, is, 

 whether these elements are also represented in such a soluble state as to be taken up by 

 plants in the quantities required by them. It is here then that the physical structure of the 

 rock, and more especially its permeability and liiirfroscopicitij are forced upon our consider- 

 ation. But hygroscojiicity is nothing but the ability to absorb moisture, the most important 

 chemical agent in nature, which brings about all those changes, of which we become aware 

 from the decomposition of rocks and their products. 



The permeability of soil is, in my opinion, as important a factorf as is the hygrometrical 

 state of the atmosphere in climatology ; in fact both are closely connected and depend upon 

 one another. A perfectly impermeable soil, if such could exist, would simply exclude all 

 phanerogamic vegetation. The degree, however, of hygroscopic quality of substrata is vari- 

 able, and therefore, the vegetation on the same is equally variable. But by studying the 

 effects which are produced by extreme conditions, we arrive at a due appreciation of such a 

 factor : degree is here a matter of valuation, but extremes are matters of fact. 



On such principles as are here laid down, I can understand, why so few plants should 

 grow on a sandbank : for the simple reason, that here the chemical elements, contained in the 

 pebbles, are not disclosed for a more luxuriant vegetation. I can understand also, why on 

 laterite and other impermeable formations, the forests should be so poor in growth, and the 

 trees so scattered, or why in a deep sandy alluvium a similar, though modified growth should 

 exist. The occurrence of calcareous plants in small numbers in a purely silicious district would 

 as little surprise me as, for instance, a raspberry or strawberry, on a Burmese hill. 



The same rock, however, of the same chemical and physical quality, will be disintegrated 

 (especially if of a more permeable nature) to a greater extent in a damper climate 

 or in damper and more shady situations, and in this case the vegetation that grows on the 

 moister locality will necessarily differ greatly. I simply point to the evergreen forests, which 

 grow in the valleys of the Pegu Yomah, and the upper mixed forests, which grow above them 

 on the same sandstone, where hardly one species out of five is found in both sorts of forests. 

 If we reject moMtire, or what is equivalent to it, water, as a chemical agent, the theories of the 

 influence of chemical compositiouj would appear to receive a fatal blow through this example, 

 but we shall learn below of other factors, which are the true causes of this change in 

 vegetation. 



Highly impermeable rocks, however, are also in very damp climates, as those of the 

 Malay islands, sterile to a greater or less degree, and especially where they embrace large 

 tracts of lands. How far impermeable formations are connected with a drier climate, I 

 cannot elucidate here clearly , but that they cause a general dryness one can perceive from 

 the laterite vegetation, which appears nearly all along the base of the Yomah in detached 

 patches, enclosed all round by permeable alluvial- beds and sandstone formations. The 

 chemical elements that compose the laterite, in which, amongst others, the great percentage of 

 hyperoxyde of iron is remarkable, do not certainly here come into play ; and this becomes 

 clear, when we find the same laterite plants again upon the calcareous compact sandstone of the 

 Prome district, a rock which may prove to differ little in percentage of oxide of iron from 

 the soft grey, but highly permeable, sandstone. I refer here to such plants as are found 

 both on the pure laterite and on calcareous sandstone. 



There is, however, a vegetative element present in the Prome flora, so peculiar to this 

 zone and so restricted, that for these plants other causes must be sought, and possibly in the 

 absence of chemical analyses they may be found in the presence of a great percentage of 

 lime, represented here in the form of fossil shells. || 



* Published in the Journal of the Asiatic Society of Bengal. 



t Amongst Indian Botanists, Griffith, in his itinerary notes, has also admitted the same, although he denies 

 the influence of chemical quality of soil. 



t Those who wish to learn more on this subject, may refer to Dr. Liebig's well-known work " Chemistry 

 adapted to Agriculture and Physiology," 2 vols. 8th edition, 1865. Much information is contained also in the 

 hook Row crops grow. By S. W. Johnson, by Kev. A. H. Church and Thiselton Dyer, 1 vol. 1869. 



I will here refer only to the Australian plateaus and to the Cape of Good Hope, as also to the Eastern 

 parts of Hindustan and Mexico. ..... 



11 A rude qualitative examination of this sandstone since made, has taught me, that it is of so calcareous 

 a nature, that it eflervesces like calcspar when treated with acids. It is, therefore, more properly called a calca- 

 eowi or marl-sandstone. It is remarkable, that the same rock, when decomposed, loses all its carbonate ol lime. 



