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4. Brief consi'derafi'ons of other agencies trhich influence rfgetiilion. 

 Before passing to the botanical description of Pegu, I have thought it might not be 

 uninteresting to notice here a number of conditions which more or less intlueiice vegetation. 

 I must, however, ask indulgence for the fact that the subjects presently to be discussed are not 

 recorded in a more consecutive form, and are treated rather heterogeneously. This want of 

 sequence arises from the fact that I wish to direct attention only to some of the more interesting 

 agencies, omitting many others. 



The consideration of the origin of Pegu plants, their probable immigration from adjacent 

 or remote countries across ancient mountain-chains, etc., has little or no value in the 

 eyes of a forester. To him it is indifferent whence his trees have come : it is sufficient 

 to know that they are present. The occurrence of wild vanille, wild tea, or rhea has more 

 interest to him than such a puzzling circumstance, for instance, as the occurrence of a speoies 

 of plantain (Mum glauca), which is found in the northern Yomah, and turns up again along 

 the southern slopes of Java a fact which sets at defiance all existing theories of tlie geogra- 

 phical distribution of plants, as no satisfactory cause whether former continuity of laud, or 

 agency of man or bird, can be assigned for its immigration. Nor does he care to consider the 

 stoange accumulation of Hindustan plants, which are found in such numbers and so unex- 

 pectedly in the Prome zone, and of which the origin* is almost as problematical as that of the 

 plantain just alluded to. 



I shall, therefore, pass from speculations to facts, and bring under review : 



(1) The influence of physical structure of soil, etc. 



(2) The influence of light. 



(3) The influence of elevation. 



(4) The influeuce of exposure. 



(5) The influence of winds. 



(6) The influence of jungle-fires. 



(7) The influence of the nature and germinating power of seeds upon the prevalence 

 of forest trees. 



(1.) The influence of the quality of rocks, etc. and that of their chemical composition is 

 differently estimated by difierent authors. While Thurmann (Essai de phytostatique applique 

 k la chaiue du Jura) admits the importance of the former only, Uuger aud others (especially 

 Sendtner in his admirable workf on the vegetation of Southern Bavaria and tliat of the 

 Bavarian Forest) have shewn in a clear and convincing manner the important part which 

 certain chemical elements play in vegetation. Schnitzlein and Frikliinger, in their work 

 on the vegetation of the Woernitz and Altmiihl, and also Bogenhard and others, look upon 

 both these factors as equally important, and to a certain degree I adopt their views. 



The physical and the chemical nature of soil act, in my opinion, reciprocally upon one another. 

 A soil consisting entirely ofsilioious sand can no more support vegetation than oil can give exist- 

 ence to aquatic plants. A crumb of bread, perfectly dry and exposed to a dry atmosphere, will not 

 be covered by PenicilUum or other mucorine growth, but let the atmosphere become damp, and all 

 conditions for the developement of fungoid growth are given. The fact that any cubic yard of 

 soil contains, after all, all the chemical elements necessary for the requirements of any 

 particular plant, may, to a superficial observer, necessarily convey the idea, that the chemical 

 composition is of no material importance to vegetation ; but this very fact, that such chemical 

 elements must be present, would a priori suggest to me an opposite opinion. 



If we know on the one hand from facts, that the organic constituents of one and the same 

 species may vary according to the chemical quality of the soil ou which the plant grew, we 

 know on the other hand the not less important fact, that there are chemical compounds, which 

 have a decided influence upon plants, either in modifying, or altogether suppressing, their 

 growth. If we syringe a plot of luxuriant meadow with a strong solution of corrosive 

 sublimate, or arsenic, we shall in a very short time see the whole vegetation on this plot 

 completely die out, although the chemical elements, necessary for the growth of tlie plants 

 that have grown here, have not been changed or removed in any way by the experiment. 

 Cldoride of sodium, or common salt, is a necessity to tidal or saline plants, but it is also fatal 

 to many inland plants, although it may be accompanied by all those chemical ingredients, 

 believed to be necessary to the nourishment of such plants. The influence of manure upou 

 plants is too well known to need illustration. 



Drs. Hooker and Thomson, in tlieir Flora Indiea ascribe this to a climate similar to that of the Carnatic. 

 I can only suggest, that most ol' these are calcareous plants. What kunkur is in Behar and Hindustan, ybsj/ shells 

 may bo in the Prome (and Ava) district. Tliis assumption becomes more probable iwe take into account such of 

 the(c plants although few as turn up agaiu ou limestone in the Martaban and Moulmein districts, aud even 

 in lower Siam. 



t This work seems to have remained quite unknown in England, although it is one of the most important 

 prodactionB in the field of geographical botany, based upon truly scientific principles. 



