276 HORTICULTURE [Box. Absts., Vol. VII, 



1929. Pickering, Spencer U. [Annual report.] Rept. Woburn Exp. Fruit Farm 17: 

 1-87. Sfig. 1920. — [Some copies of this report contain an appendix on Flocculation reprinted 

 from Proc. Roy. Soc. London A, 94:315-325. 1918.]— (1) Action of grass on trees. In pot 

 experiments the injurious effect of grass grown above the roots is the same whether the grass 

 is grown in sand or in loam and is independent of the thoroughness with which the grass roots 

 intermingle with or are separated from the roots of the trees. This is what would be expected 

 if the injurious effect is due to a soluble toxin produced during the growth of the grass rather 

 than an effect of competition for water and nutrients. Striking effects were obtained by 

 grassing over portions of orchards which had been under tillage; the crop was reduced by 5 

 per cent the first season and by 50-90 per cent the second; recovery did not follow even a 

 year after the grass was removed. (2) Experiments with soft-wooded plants. The experi- 

 mental plants were grown in pots and subjected to the action of surface growth consisting 

 of grass and numerous other plants grown in an annular, perforated tray resting on the 

 soil in the pot. A deleterious effect of one crop on another is a general action applying 

 to all plants alike, though there may be differences in the extent to which different plants 

 are effected or capable of injuring others. The nature of the toxin is unknown but it is easily 

 oxidizable and may then serve as plant food; as a result of this, soft-wooded plants may make 

 some recovery from the toxic action of other plants grown above their roots, but hard-wooded 

 plants are rapidly, and apparently permanently, stunted. The toxic effect is not due to car- 

 bon dioxide produced in the soil by the surface growth and can not be counteracted by lime 

 or by cresylic acid. The deleterious effect is reciprocal and trees were found to retard the 

 growth of grass and crops planted beneath them in a manner independent of water and nutri- 

 ent competition and shading effects. (3) Behavior of plants in masses. Plants were grown 

 in rectangular pots, some undivided and others divided into six compartments to prevent 

 root interference. Where the mass of soil is below a certain limit, the amount of plant growth 

 is independent of the number of plants, i.e., the growth of individual plants is proportional 

 to the area occupied by each provided the plants are of the same age. When plants of different 

 ages are mingled, the older plants flourish at the expense of the younger ones and the total 

 growth may be 20 per cent below the maximum possible when all the plants are of one age. 

 A difference of 4 days in the age of mustard plants reduced the total crop by this amount. 

 This effect is attributed to the toxic action of the older plants, the quantity of toxin produced 

 being proportional to the amount and vigor of the growth. Interference of the above ground 

 parts has very little effect on the amount of growth unless actual crowding occurs, since even 

 great increase of the distance between plants does not result in an increase in growth greater 

 than 15 per cent. The fact that border plants in field plots exceed the interior plants, is 

 attributed to root interference within the plot, and more rapid oxidation of the toxins at the 

 border. The inferiority of the interior plants can not be due to competition for food since 

 the same effect is observed when the plots receive applications of fertilizers in excess of those 

 which give beneficial returns. (4) Drainage and toxicity. An important effect of drainage is 

 attributed to the removal of toxins produced in the soil by the surface growth.— Freeman 

 Weiss. 



1930. QuiNN, Geo. Notes on olive growing. Jour. Dept. Agric. South Australia 23: 

 603-606. 1920. 



1931. Reed, C. A. Pecan grades and standards. Amer. Nut Jour. 11:69. 1919.— The 

 importance of a definite table of grades is realized. The number of nuts per pound is not a 

 safe criterion in establishing a grade. The author divides pecans into three groups each 

 with two standards based on diameter measurements. — E. L. Overholser. 



1932. RiNGELMANN, M. Suf la resistance du vitrage des serres. [The resistance of 

 greenhouse glass.] Rev. Hort. 92: 146. 1920.— The resistance of ordinary double glass, and 

 of cast striated glass of the same thickness is the same, as shown by an accompanying table. 

 — E. J. Kraus. 



1933. Sargent, C. S. Forty-two distinct forms of hickories. Amer. Nut Jour. 10: 20-21. 

 1919. 



