1918] CURRENT LITERATURE 113 
criterion. of durability, he recommends specific gravity, which, he says, is 
easily determined by inspection. The points to be noted are the proportion of 
summer wood to spring wood in the growth rings, and the width of the growth 
rings. If these are narrow, if the proportion of summer wood is high, and if 
the proportion of sap wood is low, the piece of pine can be considered of high 
specific gravity and therefore durable. 
DuGGar, SEVERY, and Scumitz4 have made a study of the growth of 
Macrosporium commune, Aspergillus niger, Glomerella (Gloeosporium) Gossypii, 
and Penicillium expansum on decoctions made from green string beans, corn 
meal, fresh turnips, sugar beets, dried prunes (exclusive of seed), and potatoes. 
Besides the natural decoctions, variants of these were used, containing, in 
addition to the plant extracts, different amounts of acid or alkali, cane 
sugar, potassium nitrate, and potassium acid phosphate. They found that the 
addition of sugar, nitrate, and phosphate gave in every case except one 
(Glomerella on bean decoction) increase in growth over the addition of sugar 
alone: Usually the next highest growth occurred when sugar and nitrate 
were added. Sugar alone gave a relatively slight increase over the natural 
decoction. The prune decoction seemed less favorable for growth than any of 
the others, except in the case of Macrosporium. Hydrogen-ion determinations, 
caused a pronounced shift in the other direction. It is worthy of note here 
that REEpS found an increase in alkalinity in cultures of Glomerella rufomacul- 
ans, while the writer’ has shown the same condition to hold in case of apple 
bark attacked by blister canker (Nummularia discreta). Penicillium caused 
an increase in acidity in the natural and standardized decoctions. 
From the results of an investigation of the mosaic diseases of plants, 
FREIBERG’ comes to the conclusion that the infectious substance is an enzyme 
and not a virus, as ALLARD claims to have shown in recent work on the mosaic 
disease of tobacco. FREIBERG’s reasons for his conclusion are that the infec- 
tive principle i is adsorbed by talc, and i is destroyed by concentrations of alcohol 
and b The fact that the infec- 
tive principle i is destroyed by Se caekeinde | is due, he thinks, to a specificity 
4 Duccar, B. M., Severy, J. W., and Scumrrz, H., Studies in the gag of 
the fungi. vv. The wowth of certain fungi in plant decoctions. Ann. Mo. Bot 
Gard. 4:165-173. 1917. 
5 REED, H. S., The enzyme activities involved in certain fruit diseases. Va. Exp. 
Sta. Rept. 1911-1912 (pp. 51-78). 
° Rose, D. H., Oxidation in healthy and diseased apple bark. Bor. Gaz. 60:55- 
65. 1915, and unpublished work 
7 FREIBERG, G. W., Studies in the mosaic diseases of plants: Ann. Mo, Bot. 
Gard. 4:175-232. 1917. 
