30 BOTANICAL GAZETTE [july 



Washington, plains and sand hills of Colorado, the gravel slide, 

 half gravel slide, and forest communities of the Rocky Mountains of 

 Colorado. Among other interesting observations on roots inci- 

 dental to- studies of other features, Hitchcock (21), Pammel (27), 

 and Sherff (37) might be mentioned. Very little work has been 

 done on the root systems of trees. BtJSGEN (5) was not accessible 

 to the writer. Pulling (28) describes the root systems of certain 

 trees of the northern coniferous forest, but does not attempt much 

 explanation of the phenomena observed. 



Effects of environment. — The main records of the influence of 

 soil on the extension of root systems are incidental to other sub- 

 jects^ as Cannon (6, 8), Hilgard (20), Hellriegel (19), and 

 others. Craig (12) observed the effects of frost on the root sys- 

 tems of fruit trees; Tolsky (40) made some careful experiments 

 with oats grown at 25° and 8°, respectively; and Transeau (42) 

 observed the results of different temperatures on the growth of 

 seedhngs in bog water. Cannon (10) discusses the relation of 

 temperature to rate of root growth. As to the depth of water table. 

 Cannon (7) made observations on the root systems of desert plants 

 and also on development of seedlings in relation to the water supply. 

 Cannon and Hilgard give some information on the effects of 

 drought, but the most extensive article by Rotmistrov (31) was 

 accessible only in the review in the Experiment Station Record. 

 Bennett (3) offers evidence that roots of certain land plants are 

 not aerotropic, and Cannon (8) concludes that in mesquite and 

 Fouquieria aeration within limits favors root growth and shoot 

 development. Noyes, Trost, and Yoder (26) conclude that 

 excessive CO2 is detrimental to normal root development, and 

 agree with Cannon and Free (ii) as to the importance of soil 

 aeration. 



Since the work of Nobbe (25) and Stohmann (38), Hoveler 

 (22), Benecke (2), and Tottingham (41) have done the most 

 comprehensive work on chemicals. On the whole, such work has 

 been chiefly on the roots of seedlings, and the question at once 

 arises whether the results would have been the same with mature 

 root systems. Benecke quotes Probst to the effect that "observa- 

 tions on mature plants gave results opposite to those in plants less 



