THE ECOLOGY OF THE UPPER GANGETIC PLAIN 299 



heat, what in the form of visible light, and what ultra-violet. Table II 

 shows the observed records of mean cloudiness, based on hourly 

 observations extending over a number of years ; these same records 

 are plotted in graphical form in Fig. 3. 



Mean monthly cloudiness on the scale of 0—10, for Allahabad. 



Clouds become common in June, perhaps two weeks before the 

 rains actually begin. June to September are the cloudy months. In 

 June there are densely cloudy days interspersed with days of burning 

 sunshine. During July and August the clouds are denser and more 

 persistent, but even then there are breaks when the sun shines from 

 a nearly cloudless sky with the intensity of the dry season. From 

 September on the number of sunny days gradually increases, till in 

 November the sky is cloudless or overspread with only thin hazy 

 clouds for weeks at a time. This is broken at some period during 

 December, January or early February by the " winter rains", when 

 for a short time monsoon rains are repeated on a miniature scale. 

 During most of the time from the end of the rains to the beginning 

 of the next monsoon the sun shines down with unbroken violence, 

 accentuated during March, April, and May by low humidity. 



Temperature. The climate of the Upper Gangetic Plain is 

 distinctly continental. The nearest large body of water is the Bay of 

 Bengal, more than 400 miles to the eastward. The temperature accord- 

 ingly exhibits a large range between winter and summer, and between 

 day and night, despite the fact that Allahabad is barely outside the 

 tropics. The lowest temperature occurs in December, when the 

 mean is 59.0° F. ; January is 0.3° warmer. From then on there is 

 rapid rise to a maximum of 91.6° F. in May and June. The high 

 point that should be reached in June and July is prevented by the 

 increasing cloudiness of June, and the following monsoon. In July 

 the mean temperature is 84.4°, falling to 83.0° in September. Here 

 what would be the normal descending curve is met again, and the fall 

 is rapid to the 59.0° of December. Table III shows the temperature 

 in degrees Fahrenheit by months for the year (see Figs. 1 and 3). 



