134: PERIODICITY IN VEGETATION. 
their growth. Towards midsummer they are often delayed from 
a deficiency of moisture. In general, the monthly average of 
heat will have a greater effect on plants than the annual average. 
The monthly averages exhibit a fluctuation of several degrees: 
for example :— 
January : 31°-5, Fah., 34°, 35°, 37°, 38°32, 40°66; a range of 
above 9° in seven years. 
February: 34°33, 34°, 40°, 43°, 38°, 42°:25; range of 9°. 
March: 37°25, 42°22, 42°25, 45°, 42°, 44°:5, 46°; range 
S75. 
April: 47°, 49°, 52°, 50°°5, 49°75, 53°, 49°°5; range 6°. 
May: 54°, 59°75, 56°°5, 54°, 53°°5, 63°33; range 10°28. 
June: 68°, 60°, 59°, 60°; range 9°. 
July : ‘70°, 62°, 62°; 61°;’ range: 9°. 
August: 58°66, 70°, 68°, 67°; range 11°34. 
September: 57°°5, 59°, 60°°5, 51°-5; range 9°. 
October: 45°75, 56°°5, 49°°5, 47°; range 10°-25. 
November: 43°, 44°°3, 43°, 40°82; range 3°21. 
December: 389%5, 44°, 42°°75, 41°66; range 4°:95. 
The annual averages are between 49°75 and 51°5; range 
175: 
The average monthly temperature fluctuates about 8°, accord- 
ing to the above, while the annual average fluctuation is under 
2°, and, if accurately determined by proper instruments, would 
rarely or ever much exceed one. The general average annual 
range, in any given latitude, is not probably above half a degree. 
The above results were obtained from a series of daily observa- 
tions, made at 7 a.m., 1 to 2 p.m., and 8 p.m., extending over a 
period of from five to seven years. It is probable that the ge- 
neral statement of monthly and annual temperatures is too high, 
as the thermometer was not observed during the night, and a self- 
registering instrument was not employed. This, however, does 
not affect the monthly or annual ranges. The annual average 
temperature of London and its vicinity, 7. e. within twenty or 
thirty miles of the metropolis, is about 50°. The annual average 
temperature of the south of Devonshire is probably one degree 
higher, 51°; and it appears that the temperature of the north of 
Sutherlandshire, Scotland, is 46°. The early flowering plants 
are nearly a month later in the north of Scotland than they are 
here; for example, the common Primrose, which flowers here in 
