CLIMATE AND PLANT GROWTH. 5 



veloped to a length of about 2^ inches the seedlings were transferred 

 to the receptacles in which they were grown to maturity or until 

 killed by frost. 



PLANTING, 



In order to insure luxuriant and healthy development of the plants, 

 those observed throughout the season were grow^n in substantial heavy 

 galvanized iron potometers. 



To protect them from injury by animals, hail, etc., the plants were 

 grown under wire screen of the mesh usually used on screen doors, 

 supported by light wooden frames. These screen frames decreased 

 the light intensity between ^0 and 50 per cent. 



Water was added to the potometers as needed, the need being de- 

 termined by the weight of the cans. In no case was the soil allowed 

 to dry to a point approaching closely its wilting coefficient, nor was 

 it at any time flooded. In watering, the potometer was brought up 

 to its original weight. The first watering was done about a month 

 after planting and the second 15 days later. From then on it became 

 necessary to add water about once a week in all stations and oftener 

 in the drier situations, 



THE POTOMETERS. 



The potometers were 17 inches high and 14 inches in diameter, 

 and had a capacity of 90 pounds of air-dry soil, which provided a 

 soil mass at all times affording ample space for the proper develop- 

 ment and spread of the roots, • The cans were fitted with lids of 

 the same material as the cans, and five holes, | of an inch in dia- 

 amter, were punched in each for the plants, (Fig. 1, top view.) 

 In the center of the cover a hole 1^ inches in diameter was provided, 

 which was used in watering and was fitted with a cork stopper and 

 a capillary tube bent at right angles. 



Before placing the lid, sufficient soil was removed in the center of 

 the can to make room for a granite-ware receptacle 4 inches in height 

 by 5 inches in diameter, perforated centrally in the bottom and un- 

 derlaid with 1^ inches of gravel, as shown in the sectional view of 

 figure 1. This greatly facilited the addition of water. To add the 

 water, a flask of known capacity Avas inverted and the water per- 

 mitted gradually to percolate into the soil. 



After the lids were placed, the spaces between the rims and cans 

 were closed by securely sealing them over with strips of surgeon's 

 adhesive tape 2^ inches in width. The adhesive tape was then coated 

 with shellac to prevent its loosening when wetted by rain. The 

 method used in sealing and watering the plants was one devised by 

 Briggs and Shantz,^ modified somewhat to suit special conditions. 



1 Briggs, Lyman J., and Shantz, H. L. The water requirements of plants. U. S. Dept. 

 Agr. Bur. Plant Ind. Bui. 284:8-14. 1913. 



