238 THE JOURNAL OF INDIAN BOTANY.
The average rainfall in the Sat Tal valley as recorded by Mr.
A. 0. Evans, proprietor of the estate, for the eight years from June,
1913 to May, 1921 was 85.02 inches. This corresponds pretty
closely with the figures in the Naini Tal Gazeteer for the rainfall at
Kathgodam at the foot of the outer range, 91.27 inches, and at Naini
Tal about five miles from Sat Tal to the north-west and at an altitude
of about 7000 feet, 97.49 inches (8). These places all lie in a general
way on the outer slope of the outer range, for the highest peak of
Sat Tal is at the north of the valley. The inner valleys of the
Himalayas have considerably less precipitation.
The altitude above which frost is severe enough to affect vegeta- tion is approximately 4000 feet. Sat Tal has an occasional hoarfrost, but the temperature rarely gets down to the freezing point.
Seasonal Periodicity of Vegetation.
The distribution of the rainfall by months is shown in Fig. II, 84 per cent, of the rain falls in four months — June, July, August and September. Hence there is in all the formations a striking seasonal periodicity based on the water supply. This is most marked in the lower or monsoon forest formation where the effect of the dry period is most intense. At the beginning of June, vegetation is at a compa- ratively low ebb, the monsoon forest trees being leafless and herbs being not much in evidence. With the first rains there is a marked revival of activity. The trees which have to this time remained leafless burst into leaf, a wealth of annual and fleshy rooted perennial herbs spring up, and there is germination of many tree seeds upon the forest floor, e.g., those of the Bauhinias.
With the close of the rainy season much of the herbaceous vegetation ripens its seeds and dies to the ground. October brings a wealth of composite and labiate herbs, including goldenrods, asters and groundsels, which remind one of the forest floor of a climax oak forest in Europe or America. Already some of the monsoon forest trees such as Bombax malabaricicm, Qaruga pinnata, and Erythrina suberosa are losing their leaves. Winter deciduous trees of the oak forest, such as Primus pucldum and Pyrus pashia, become leafless about the same time. No part of the winter is too cold for the vege- tative activities and even for the flowering and fruiting of much of the vegetation. Prinsepia utilis, a widespread pioneer rosaceous shrub of the oak forest, has festoons of blossoms in midwinter. About Feb- ruary the candle-like spikes of Sapium insigne appear.
From March to May is the hot season. Trees blossom profusely during the early part of this season, conspicuous among them being the legumes of the upper monsoon forest. Bauhinia variegata puts
