ANNUAL REPORT, 1931 207 



tice, it is probable that the necessary aeration of the soil can occur only through 

 the surface of the soil. It has been found in preliminary experiments that air 

 under slight pressure passes through the wall of a dry flower pot very slowly, 

 and yet this rate is thirty times as fast as the rate through a moist wall. 



The reaction of the soil in regard to hydrogen ion concentration is not altered 

 by conditions in non-porous containers any more than it is in clay flower pots. 

 The soils in paper, glass and porous clay containers in which tomato plants had 

 been growing for 40 days all reacted the same to tests for acidity. The reaction 

 of soils in which geranium and petunia plants were grown for nearly four months 

 in glass and metal containers without drainage holes, was no different from that 

 of soil in the regulation clay flower pots. The reaction of the soil in paper pots 

 was not affected by keeping the pots on moist beds of cinders, soil, or sand or 

 on dry benches of wood and cement. 



Influence of Light Quality on Plant Growth. (A. V. Osmun). In the 

 experiment to test the effect of Vita glass on plant growth and development, the 

 results were comparable with those of last year. Under Vita glass, radishes 

 seeded January 14 and harvested March 17 averaged 11.3 per cent heavier than 

 those grown under ordinary glass. Lettuce transplanted March 16 and harvested 

 May 21, averaged 14.2 per cent lighter in weight under Vita glass than under 

 ordinary glass. There was no appreciable difference in compactness of heads 

 between the two lots of plants. At no time since the experiment was started in 

 1928, have diff'erences been so marked as in the first tests, when the results were 

 strikingly in favor of Vita glass. In every test but one with radish. Vita glass 

 has given an increase in average weight of plants, while in only one test has 

 lettuce averaged heavier when grown under Vita glass. 



Plant Diseases Observed in 1931, Not Heretofore Reported in Massa- 

 chusetts. ((). C. Boyd). 



^^'ilt and black-rot of the following cucurbits caused by Mycosphaerella 

 citndlina (C. O. Smith) Gross.; vine infection only of summer squash and musk- 

 melon; fruit infection only of cucumber; both wilt and black-rot of winter squash, 

 pumpkin, cushaw, and vegetable marrow. 



Leaf-spot of winter squash, pumpkin, cushaw, vegetable marrow, and cucum- 

 ber, caused hy Bacterium citciirbitae Bryan (determination of organism by Mary 

 K. Bryan, U.S. D. A.). 



Leaf-spot of cucumber and muskmelon caused by Septoria cucurbitacearum 

 Sacc. 



Bacterial .seedling blight of cucumber and summer squash (organism unde- 

 termined) . 



Wilt of okra caused by VerticilUitm alboatrum Reinke & Berth. 



Leaf-spot of turnip caused by Bacterium maculicolum McC. 



Leaf and pod-spot of pea (bacterial, undetermined) . 



Dwarf or crimps of strawberry caused by the nematode, Aphelenchus jragariae 

 Ritzema-Bos. (determined by G. Steiner, U. S. D. A.). 



"Stunt" or "die-out" of strawberry, suspected of being due to the virus of 

 the true Yellows disease; observed only in Marshall berries. 



Leaf-blight and rhizome-rot of iris caused by an unidentified bacterium. 



Unusual Outbreaks of Previously Reported Diseases. (O. C. Boyd). 

 Pusicladium scab of willows, rust and Gloeosporium leaf-blight of American ash, 

 leaf-blotch of horse-chestnut, apple scab, peach bacterial-spot, brown-rot of 



