( 14 ) 



All the above remarks hare reforenoe more to the general growth and habit of trees 

 than to their nature as species. This latter is tlie oritioal question, for although even modern 

 experiments tend to shew, that such a marked influence ou the specific value of a plant does 

 exist, they cannot shew that such is a general rule. 



As far as my own experience in tropical countries goes, I can state, that a formation physi- 

 cally nnd chemically different, if of some extent, produces everywhere a flora, not only pliysiog- 

 nomically but also specifically different, but this is not the case wliere only small patches of 

 such a different formation occur. While many plants pertinaciously affect a certain soil, a far 

 greater number belong to a class, termed soil-vague, and others are in one district soil-vague and 

 under difierent climatic conditions soil-steady. Only careful analyses of the soils and of the 

 plants themselves can in such oases settle the question. I do not advocate the theory that 

 a species is restricted to a certain soil, but I believe that the same species can occur on any 

 soil, but it cannot, if chemical conditions are contrary to its requirements, support itself as 

 such for successive generations : it will succumb, or lose reproductive power,* or modify its 

 habits more or less.f Thus tliose oharacteristical botanical combinations are produced, which 

 form the most interesting portion of phytogeography. 



This would have been the place to remark on representative species, which occur on the 

 various formations of Pegu, and more especially to contrast those that occur on permeable 

 and impermeable strata, but in doing so, I should have to enter again into scientific spe- 

 culations, and I really fear that I have already far too much extended the above notes. 

 But the importance of the soil question to a forester in Pegu must be my excuse, and I 

 shall have an opportunity in the second part of my report to point out, that large sums 

 might have been saved, had this question been always carefully considered in timber plan- 

 tations. 



In considering the physical structure of substrata, &c., we have to observe other forms of 

 soils, such as sand fine or coarse, loose conglomerates, fine clayey or loamy soils, gravels, 

 shingle, &c. For the sake of brevity, I shall only separate the sandy from the clayey soils, 

 for my principal object is to show the general effect of cohesion of rocks and not to specialize 

 all the intermediate conditions. The sandy or gravelly soils, if poor in aluminous ingre- 

 dients, bear as a rule Eng'forests, with certain peculiar additions, such as Cycas, Diptero- 

 carptis grandifoUus, &e, If rich in clay, they still continue to possess the laterite character 

 along the drier Irrawaddi side ; but along the damp Eastern slopes of the Yomah, they also 

 bear high growing moist forests. The clayey sand or loam soils are, in fact, favourable 

 to the growth of trees and plants generally, and it is on such a soil, that we see the 

 finest wood-oil trees, as Dipterocarpus alatus and D. kevis, along with Ka-Thitka (Fentace 

 BurniMiica) . 



Fine clay, if very stiff, becomes to a certain degree impermeable, and therefore fit for 

 the support of the low forests. But a more porous clay, with or without fine silieious sand, 

 especially if very deep, generally produces a peculiaj shortness of stem, and a comparatively 

 large developement of crown, as can be observed everywhere in the savannah-forests. But 

 the trees in the lower mixed forests, on the alluvial strata, are also comparatively short in 

 stem and of irregular growth, branching out low down. The number of plants, that grow 

 in Pegu, is so great, that it would be difficult to enter into specialities, and to say which 

 species are peculiar to clay, and which to other soils, and if I were to distinguish the soils 

 as minutely as Thurmann did, I fear I should make the understanding of the influence of 

 mechanical structure of soils upon plants only the more difficult. 



As porous clay soils in Pegu are chiefly alluvial, it is sufficient to direct attention to 

 the vegetative combinations, that are represented on alluvium, such as the alluvial mixed 

 forests and swamp forests, &c.. 



There is a peculiarity, which all the larger alluvial plains of India show, and which it may 

 be interesting here to notice : namely, the great paucity of species, and more especially of 

 species of trees. Alluvium has hardly any plants peculiar to itself, except those which 

 occur in the littoral and swamp forests, both which combinations must be attributed to other 

 causes, viz., either to the saline quality of the soil, or to superabundance of water. Nearly 

 all plants, if not introduced and spread, are found also on the surrounding older formations, 

 so that there can be little doubt that the plants growing on alluvium, have immigrated from 

 the surrounding non-alluvial lands. Owing to the uniform chemical and physical qualities 

 of alluvium, only such plants would thrive well here, as are adapted for such a uniform aud 

 comparatively poor soil : hence a great many plants of the surrounding land became ex- 



With regard to this, compare Wiegmann's and Polstorf s trials, which are taken up also in Liebig's Che- 

 mistry, p. 331 Sq(j'. A remarkable example is aftbrded by the K. Botanic Garden, Calcutta, which is so rich in 

 woody plants that have become impotent for the reasons above mentioned. Those usually flower yearly without 

 producing gemiinable seeds. There are only a few species amongst them, where heteromorphism, of the repro- 

 ductive organs can be adduced as the cause of sterility. 



t The mimetic analogies of plants, so much talked of at the present day, find their solution in the soil 

 question, not in " mimicry." 



