32 MASS. EXPERIMENT STATION BULLETIN 339 



cotton may also be used. Ceramic materials have been tested, but none were 

 as efficient as fibrous materials. Sponge rubber supplied free water which was 

 detrimental to the plant as it caused a waterlogged condition in the soil. 



The Water-Supplying Power of Soils. (L. H. Jones.) A relatively 

 rapid method of determining the water-supplying power of a soil at different 

 percentages of its water-holding capacity shows promise of being fairly accurate 

 and practical. Measuring in seconds the time it takes for moisture to strike 

 through blotting paper held to the soil by a glass weight shows increased time 

 with soils of high water-holding capacity and decreased time with soils having 

 a low wilting coefficient. 



Selocide as a Plant Stimulant. (P. F. Eobula and L. H. Jones.) A 

 spray material commercially called Selocide and used to control red spider 

 has produced on roses a general increase in height of plant, length and breadth 

 of leaves, and thickness of stem. Tests with tomato plants indicate that the 

 stimulation is effected by volatile materials in the spray which find access to 

 the plant through the atmosphere. 



Effect of Soil Temperature on a Chlorosis of Gardenia. (L. H. Jones.) 

 Observations of gardenia plants in several environments indicated that, when 

 all other factors were equal, a low soil temperature induced an intervenal chloro- 

 sis of the top leaves and that longer exposures to low soil temperatures accentu- 

 ated the condition to the point where the leaves were entirely yellow and often 

 almost white. Raising the soil temperature caused a reappearance of green 

 which was first evident in the new-forming leaves and gradually worked down 

 the stem to the older leaves. 



Plants grown in soil temperatures starting at 8° C. and increasing in 2° steps 

 through 32° showed yellowing induced at 18° and less, with no signs of yellowing 

 at 22° and above. 



The size of the gardenia leaves was definitely tied up with soil temperature 

 and not with air temperature. 



DEPARTMENT OF CHEMISTRY 

 W. S. Ritchie in Charge 



Cooperative Analytical Service. (The Department.) Cooperative work 

 with the several departments has been continued. The analytical service to 

 the investigators at the Waltham Field Station has been the major and most 

 important activity. Determinations for iron, manganese, copper, phosphorus, 

 and soluble and insoluble ash were made in the study of the cause and preven- 

 tion of chlorosis in gardenias. 



Testing Analytical Methods. (The Department.) The work aiming at 

 the improvement of the methods for determining iron, copper, and iodine has 

 been continued. Considerable time was spent in collaborating with the Asso- 

 ciate Referee of the A.O.A.C. in charge of developing suitable methods for 

 determining copper in foods. 



The obligation of investigating and attempting improvement in the methods 

 for zinc (as associate referee ) in foods was assumed. A survey of the methods 

 for determining zinc has been made and work begun, but no collaborative work 

 has been attempted as yet. 



The effort to improve the methods for determining iodine in foodstuffs 



