Nov., 1911.] Climatic Conditions and Plant Growth. 
393 
the first samples were taken. Station 5 was of the beech forest 
type. The surface is nearly level at all of the stations. Stations 
1 and 2 are 35 rods apart, and stations 3 and 4 are 15 rods apart. 
Stations 3 and 4 are 656 feet lower than stations 1 and 2, and 
about one-third of a mile distant. Station 5 is a few rods distant 
from station 2. 
The difficulties of studies of soil moisture are very great owing 
to daily variations of temperature, of evaporation rate at different 
hours, and other variable factors. While we have given the per cents 
of water based both on moist soil and dry soil, we shall use in the 
discussion only the former. A given per cent of water in one soil 
may mean a very different condition for the plant than the same 
per cent in another soil, and a given per cent in any soil affects 
different plants differently. Clay soils will hold approximately 
40 to 50 per cent of water; and most land plants can not secure 
water from clay when the per cent falls below 9 or 10, while few if 
any can secure water from such soil containing less than 6 per cent. 
Loams and humus will hold approximately 50 to 65 percent of 
water; and most plants cannot extract water when the percent 
falls below 10, and few if any when it falls below 6. Sand will 
scarcely hold more than 15 per cent of water, but most plants can 
still obtain water from sand when the per cent falls below one. 
Plants that can obtain sufficient water only when the per cent is 
high are hydrophytes, those that can obtain it when the per cent 
is moderate are mesophvtes and those that can still obtain it 
when the per cent is low are xerophytes. 
It will be seen from the table above that the soil moisture on 
October 8, 1908, at station number 1 had reached the point where 
mcsophytes, which include most of the land plants of the region, 
whether wild or cultivated, would have great difficulty in securing 
water from the clay at a depth of 36 cm. At station number 2 
on October 15, 1908, mesophvtes could secure water from the clay 
at depths of 56 and 41 cm., but not at a depth of 13 cm., where 
even xerophytes might fail utterly to secure soil moisture. At 
station number 3, on October 21, 1908, mesophytes could secure 
soil moisture at 50 and 26 cm. deep, but with some difficulty. 
But at the same station, on July 8, 1909, mesophytes would have 
no difficulty in securing abundant soil moisture at these depths. 
At station number 4, on November 6, 1908, garden plants should 
be able to obtain soil moisture, though probably with some 
difficulty. But in this station, on July 8, 1909, garden plants 
would have no difficulty in securing sufficient soil moisture. At 
station number 5, in the heavy beech woods, most plants would 
not be able to secure soil moisture from the clay soil at depths of 
29 and 40 cm. on December 23, 1908, while moisture could be 
secured easily at such depths on April 19, 1909. Hundreds of 
stations and "daily testings throughout the season would be neces- 
