700 JOURNAL, BOMB A Y NATURAL HISTORY SOCIETY, Vol. XVII. 



imply that temperature is superfluous ; on the contrary, everybody 

 knows how necessary a condition temperature is for the development 

 of plant life, not only in the temperate zone, but also in the tropics. 

 What we wanted to say was only this : Temperature in the tropics is 

 usually so uniform throughout the whole year that its influence does not 

 cause any great disturbance in the course of vegetable life as determined 

 by the action of rainfall, clouds and humidity. Temperature is, thus, as it 

 were, hidden behind the hydrometeors. The further we go northwards 

 starting from the tropics, the more distinctly marked is the influence of 

 temperature. Thus we see that in North-West and Central India, 

 and in the Upper Gaugetic Plain, the curves of the flowering times, 

 after having reached their maxima, are strongly influenced in their 

 course by the temperature ; not so in Bombay and Burma. The curves 

 of the flowering times show at every point their dependence upon the 

 hydrometeors, whilst they are not affected at all by the temperature. 



A good illustration of how the flowering season is determined by the 

 temperature in extra-tropic regions, is the vegetation of Simla. I 

 collected the data from the " Flora Simlensis " by Colonel Sir Henry 

 Collet. In this flora those plants are described which can be seen in 

 Simla and on excursions from this town to Mushobra, Mahasu, Shali 

 Peak, Fagoo, Narkunda, Huttoo, Baghi Forest, Sutlej Valley down 

 to the hot springs near Suni. 



" The climate of the district exhibits considerable variations at 

 different elevations and exposures. In round numbers there is a total 

 difference of 8,000 feet in elevation. From observations near Simla, 

 at about 7,000 feet, the mean temperature of January, the coldest 

 month is 40 o, 6 Fahr., and of June, the warmest month, 67 0, 1, whilst 

 for the year it is 54°'86. The lowest temperature recorded, 26 c, 6, 

 occurred on two days in February 1882. Snow falls from December 

 to March, and not infrequently lies for several weeks. The period of 

 greatest rain is from June to September, with an average of 52in., 

 whilst the fall for the whole year is 70in. There is a considerable 

 decrease in the rainfall northward ; at Kotgarh, for example, it is little 

 more than half that of Simla." 1 



The data as to the flowering season given in the " Flora Simlensis" 

 are nearly complete, and we would, therefore, be able to get accurate 

 results, if some meteorological observations made in the surroundings 



4 Coll«t : Flora Simlensu. Introduction. 



