1917] AGRICULTURAL BOTANY. 733 



The effect of insecticides on flowering plants, A. F. Shreibeb (Rchkeibeb) 

 {Trudy Biuro Prikl. Bot. {Bnl. Airpl. Bot.), 9 {1916), No. 4, pp. 115, 176).— The 

 spraying of Calendula officinalis with a decoctiou of aloes and Yeratrum alhum 

 for the control of the cabbage moth {Mamestra brassicw) is said to have shown 

 no unfavorable effect on the flowers or the development of seeds. 



Snow cracks on trees as an indication of the amount of bending, T. 

 Maekawa {Bot. Mag. ITokyo], 30 {1916), No. 353, pp. 179-184, pi. i).— The 

 author has recorded his observations on the effects of wind in cracking the ice 

 and snow on the base, body, and branches of different species of trees during 

 the progress of a violent snowstorm in Sapporo, Japan, February 24, 1915. 

 The meteorological data for the period are also detailed in connection there- 

 witli. 



The ecological significance of soil aeration, W. A. Cannon and E. E. Fbee 

 {Science, n. ser., 45 {1917), No. 1156, pp. 178-180).— -The authors report inde- 

 pendent laboratory investigations on the relation of plant I'oots to the composi- 

 tion of the soil atmosphere and especially to a deficiency of oxygen or excess 

 of carbon dioxid in this atmosphere. 



Basing their conclusions upon these experiments, the authors consider it 

 probable that soil aeration must be added as a factor of no less importance in 

 plant growth than temperature and water. In many semiarid regions shallow 

 basins without outlet occur, the central portions of which are flooded during 

 the rainy seasons but are dry for most of the year. It is characteristic of 

 these regions that they are void of plant life during most of the year and that 

 no perennials are to be found in the lowest places, even where there is no 

 excess accumulation of salts in the soil. It is suggested that the probable 

 reason for the absence of plant life in such regions may be directly traceable 

 to insufficient soil aeration at a time when the soil is suitably moist and at a 

 temperatux'e suitable for the growth of plants. About these playas are fre- 

 quently observed well-marked bands or zones of plant life and it is thought 

 that tliese represent the unlike response of the roots of the plants comprising 

 the difterent zones to the atmosphere of the soil. 



Distribution of the cacti with especial reference to the role played by the 

 root response to soil temperature and soil moisture, W. A. Cannon {Amer. 

 Nat., 50 {1916), No. 595, pp. 435-44^) .—-This is an examination of the evidence 

 obtainable as drawn from various sources, one discussed at some length in 

 this connection being the report of the Australian Prickly Pear Traveling Com- 

 mission (E. S. R., 33, p. 134). 



While soil moisture is an indispensible condition for the presence of cacti, 

 temperature appears to be a very important limiting factor. Shallow placing 

 of the roots subjects the plant to both high and low extremes of temperature 

 and gives it access to the moisture resulting from very slight rainfall. An 

 effective growth takes place only at relatively high soil temperatures when a 

 certain but highly variable amount of moisture is present in the soil. The 

 determination of the superficial position of the root system of cacti is thought 

 possibly, from studies not yet published, to result from the plant's response 

 to the oxygen supply of the soil. 



Osmotic pressure in roots and leaves of plants with respect to the moisture 

 contents of their habitats, V. S. Il'in (Iljin), P. S. Nazakova (Nasakova), 

 and M. K. OsTKovsKAfA {Isv. Imp. Akad. Naulc {Bui. Acad. Imp. Soi. Petro- 

 grad), 6. ser., 9 {1915), No. 8, pp. 749-768).— The authors have constantly ob- 

 served a very close connection between the degree of osmotic pressure and the 

 amount of moisture placed at the disposal of plant cells. They find that the 

 higher the moisture content of the soil, the lower is the osmotic pressure in the 

 roots. It is lower in meadow plants than in prairie (steppe) plants and stiU 



