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In the Prome district, the heat and dryness is considerably greater than in the Irrawaddi 

 and Sittang districts ; for although I had in the Sittaug valley at the end of April thermome- 

 ter readings of 104 to 108, and on one occasion even 1 08 in tlie shade, these were exceptions ; 

 while during my stay in the Prome district (in Marcli) the thermometer in the shaiie at 

 midday never stood below 100", but remained almost stationary between 101 and 108 till 3 

 or 4 p. M. The sky was then so hazy, that the sun after 4 p. m. regularly, and not seldom^ 

 during the whole day, appeared only as a large red disk emitting a dull light, hardly equal 

 in intensity to that during a partial eclipse. The temperature in the shade and in the sun 

 shewed a difference only of 1 J to 2 degrees, and I often worked on such days at my table 

 exposed to the direct sun-beams without feeling any more discomfort than in the shade (if 

 such a thing really can be had at this period in the Prome forests). 



While such a drought reigns in the open country and on tlie ridges, dew falls in the 

 narrow valleys of the eastern slopes of the Yomah and in the Martaban hills, where evergreen 

 forests skirt the streams, often so heavily that one becomes quite wet when marchinw 

 in the early morniirgs through the herbage along their bank. But after an ascent of a 

 hundred or two hundred feet we meet with the same dryness again in the deciduous forests, 

 as in the open lands. It is here that we can almost every morning observe a white sheet of 

 vapour in the depths of the valleys resting on the forests, which enables us to appreciate 

 clearly the role which evergreen forests play in the attraction of tlie currents of vapour. 



Tiie vicinity of the sea is always accompanied by a greater degree of dampness, especially 

 if no dry land-winds check its influence. It is often remarked that liigh level plants, such as 

 Pohjpodium Dipteris, Rhododendron, 8fc., (growing in Java at above 4000 feet elevation) 

 grow along the western coast of Sumatra, Banca, etc. almost down to the edge of the sea. 

 A more careful inquiry into the true circumstances would only shew that they grow there in 

 sheltered damp gorges, where the temperature is moderated by moisture to sucli a degree, that 

 the difference between the two stations is but small or merely nominal. Nor is elevation al- 

 ways an exponent of lower temperature. What Professor 0. Seudtner has shewn to be the rule 

 in the Bavarian Alps, viz., that the temperature on the top of hills or ridges is higher than ia 

 valleys of the same elevation, is also and to a more marked degree true in the Pegu hills 

 (and generally in the tropics). One has no need to consult his instruments : this difference 

 of temperature is great enough, not only during the day, but still more so at night. Any 

 one, who has encamped one night in a valley and the following night on an exposed ridge, 

 may have made the observation. When sleeping at the end of February in the Gryo-Gyo val- 

 ley, at the base of the Kambala toung, I required a blanket ; but 2000 feet higlier up near the 

 crest of the ridge, the nights were sultry and rather oppressive. The thermometer fully con- 

 firmed this, for while it stood at the lower station at oOj" to 60 before sunrise, it was at my 

 hill-camp as high as 70^ to 74 at the same hour of the day. In a similar way, tlie differ- 

 ence of temperature at the two stations at midday amounted to from 2 to 3 degrees in the 

 shade. I have also observed similar great differences* of temperature between hill and 

 valley stations in other parts of the Pegu Yomah as well as in the Martaban hills. Such 

 observations, however, were all made during the hot and dry season, and I have reason to be- 

 lieve that during the rains the differences are either nominal or less marked. With such facts 

 before us, it need not surprise us, if we see, amongst many others, Gleichenia dichotoma, Pteris 

 aquilina or Bkchnum orientalc, a perfect nuisance in the plains of Java, while in Pegu tliey appear 

 only above 2000 feet elevation ; or that, for example, Lmostoma pauciflorum or Vdccmiuiii should 

 be found in Singapore and Sumatra on laterite ground at sea level, while in Burma it grows 

 in the pine forests, on primary substrata at elevations of from 3000 to 4000 feet and upwards. The 

 fact that pine forests (as I learn from Dr. F. Mason) are met with in Tennasserim so low as at an 

 elevation of only 500 feet, is no doubt to be explained by the same cause. On the other hand 

 we can now correctly understand, why so many plants, (especially trees) which are high-level 

 plants in the Khasya hills, are met with in the deep gorges of the Pegu Yomah at low eleva- 

 tions ; or why so many plants, specifically identical, should be found in the Malay peninsula, 

 and even Java, and should re-occur in the damp tropical valleys of the Himalayas. 



While in the above examples, moisture, and as a consequence of it lower temperature, 

 are the chief although not sole conditions for the existence of those plants, we meet with 

 another set of plants in Pegu, which although usually looked upon as temperate forms 

 vegetate and develope themselves in the hottest and driest season of the year. It ia 

 in March and April, at a temperature of 120" to 130 and even higher in the sun, that we 

 see alon"' the banks of the Irrawaddi in flower and fruit Ranunculus sceleratus, Veronica Becca- 

 bunga, Artemisia carnifolia, the various species of Fohjgonum, Riunex, etc. and along the 

 Ganges and Bramapootra in Bengal these are accompanied by Rom, Poientilla, Covhlearia 

 flam, Juncus, Polypogon, etc. ! Now here it is evident tliat these plants, although growing ia 

 moist stations, are not hygroclimaticsf at least not tropical hygroelimatics. 



Railiation of insolated heat must be brought into account here. 



t In fact, all temperate and European forms in Lower Bengal, as Cardamine, Lalhyrus, Vicia, etc. come 

 up only during the dry cold ueasou. 



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