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 jDlants 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 mesophytes 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, 190S, at station number 1 had reached the point where 

 mesophytes, which include most of the land plants of the region, 

 whether wild or cultivated, would have great difficidty in securing 

 water from the clay at a depth of 36 cm. At station number 2 

 on October 15, 190S, mesophytes 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- 



