22 BOTANICAL GAZETTE [JULY 
which falls in the afternoon and leaves the ground wet at night 
sinks into the soil and does the plant much more good than does} 
that which is followed by a clear sky and rapid evaporation. 
A study of the rainfall record shows that much more rain falls” 
during the afternoon than during the forenoon. During the months — 
of May, June, July, and August, 1904, 72 per cent. of the rain fell 
in the afternoon; while 71 per cent. of the hours during which rain — 
was falling were in the afternoon. The sunshine record (fig. 6) also 
makes this plain. : 
Relative humidity—A deposit of dew is extremely rare. The 
relative humidity therefore seldom reaches 100 per cent. except 
during showers. During the day it is generally low, often being | 
as low as I per cent.; on account of this, rain or snow is soon evapo- — 
rated. The relative humidity is especially low during winter when 
there is little rain and when during the day the temperature often 
rises to 16°-20° C. The following table gives the relative humid- 
ity for each month of the year 1904; and fig. 2 illustrates the dai 
variation. 
= \ weclze /yoy | Se as E 
7, Al we a 
SCNSEE EEE 
x nena P 
~ 6m s blem A b\4m 
Fic. 2.—Daily variation in relative humidity. 
Jan. | Feb. | Mar. | Apr. May | June | July Aug. | Sept.} Oct. | Nov. Dec. 
—— < —— 
Masimum. cg G0). Boe} Foo. | eon} 206 04 90 95 | 100 | 100 89 | 100 
p aeereeigae ek I 8 6 I Ir 12 9 21 13 12 12 5 
verage...... 47 41 42 
44.) 58 [Sa st 2 ee gs | oe 1 ee 
MES eae BoC! oe” 
Wind. —The chief importance of wind is its effect upon the trans- | 
piration of the plant and upon the water content of the soil. The 
