NOTES AND ABSTRACTS. 
22/ 
depleted as a result of adsorption of solutes by the plant. An extension of our 
knowledge of soil solution in all its dynamic aspects will lead to the greatest 
advance in knowledge of fertility of soils. — A . B. 
Soil Solution and Soil Extract. By D. R. Hoagland, J. C. Martin, and 
G. R. Stewart (U.S.A. Jour. Agr. Res. xx. No. 5, Dec. 1920, pp. 381-396). 
— The composition and concentration of the soil solution undergoes very great 
alterations as a result of seasonal changes, crop growth, rainfall, bacteria etc. 
A soil extract is composed largely of solutes present in the soil solution plus sub- 
stances dissolved from " adsorbed " or easily soluble components of the soil. 
This last fraction depends on the concentration and composition of the soil 
solution, since the solutes of the latter exert a depressing effect upon the solu- 
bility of certain soil constituents. A new method is suggested for indicating 
the relations between the chemical elements of the soil solution. Extracts were 
prepared which did not change appreciably in composition and concentration 
on contact with the soil. The consideration of the equilibra involved suggests 
that the ratios between most of the important elements are very similar in 
concentrated soil extracts and in the soil solution. Analyses of suitable soil 
extracts and determinations of freezing-points may frequently permit a calcu- 
lation of the concentration and approximate composition of a soil solution. 
Various methods have been compared, and in seasonal studies extracts should 
be made with the smallest proportion of water to soil and the time of contact 
limited to that necessary for thorough admixture ; 1 in 1, or 1 in 5 extracts are 
convenient and satisfactory. The soil solution fluctuates in composition and 
concentration with every environmental change and crop growth. 
A short bibliography is appended. — A. B. 
Soils, Temperature of Freezing. By Geo. Buoyoucos (U.S.A. Jour. 
Agr. Res. xx. No. 4, Nov. 1920, pp. 267-270). — The general impression 
is that when the temperature of soils falls slightly below o°C. they freeze ; that 
is, the soil moisture is converted into ice. In actual practice, however, it was 
discovered that it is almost impossible to freeze the soils when they are cooled 
only slightly below the freezing-point. They have to be cooled down at least 
i° C. below their true freezing-point, and then vigorously agitated. The amounts 
of cooling that mineral soils are able to withstand without freezing is — 4'2°C. 
and peats about — 5°C. Possibly this difference is accounted for by the difference 
in the size of the soil particles. The ability of soils to resist freezing even when 
their temperature is much below the freezing-point throws new light on questions 
of temperatures of soils in cold seasons, and therefore upon the physical, 
chemical, and bacteriological processes going on in the soils in winter. — A. B. 
Stock, Evolution of the Double. By Miss E. R. Sanders (Jour. Gen. xi. 
pp. 69-74 ; April 1921 ; figs.). — Notes the occurrence of twinned flowers in stocks, 
and accounts thereby for the statements that semi-double flowers occur at 
times. — F. J. C. 
Strawberries. By A. J. Olney and C. W. Mathews (U.S. Agr. Exp. Sin., 
Kentucky, Bull. 216, pp. 67-94, illus.). By G. M. Darrow (U.S. Dep. Agr., Eastern 
U.S. Farm. Bull. 1028, 50 pp. ; 18 figs.). By G. M. Darrow (U.S. Dep. Agr., 
Western U.S. Farm. Bull. 1027, 29 pp. ; 16 figs.). By G. M. Darrow (U.S. Dep. 
Agr., S. Atlantic and Gulf Coast Farm. Bull., 1026, 40 pp. ; 21 figs.). — Describe 
the methods of growing strawberries in the different regions. The strawberry 
may be grown successfully upon almost any type of soil, provided it is well 
supplied with moisture and at the same time well drained. — F. G. A. 
Tobacco, Fusarium-Wilt of. By J. Johnson (U.S.A. Jour. Agr. Res. 
xx. No. 7, Jan. 1921, pp. 515-536 ; 5 plates). — A disease of tobacco pre- 
viously undescribed has been found to occur in Ohio and Maryland. It is 
characterized by yellowing and wilting of the foliage, the vascular system 
becoming brown or black. A species of Fusarium can be easily isolated from 
the discoloured area, and seedlings may be infected with this fungus. The 
organism appeared to be closely related to Fusarium oxysporum (Schlecht) Wr., 
but has some morphological and physiological differences. Infection has been 
secured with two strains of F. oxysporum from potato to tobacco, but not with 
tobacco strain on potato. The author suggests the name F. oxysporum var. 
nicotianae, n. var., for this organism. The conditions favouring infection are soil 
infectation, wounds in host, high soil temperature (28-3 i°C), and a susceptible 
variety of tobacco. White Burley variety is most susceptible, while Havana 
Seed and Cuban varieties are amongst the most resistant. The most hopeful 
means of control is the development of non-susceptible varieties. 
A short bibliography is appended. — A . B. 
