(J02 JOURNAL OF FORESTRY 



3. How are plants other than hog xerophytes inhihited from bogs? 



4. What are the possible sources of toxic substances in bog water? 



5. How do toxic substances in bog water act on plants? 



A Summary of Bog Theories. Plant World, vol. 9, No. 10. October, 1916. 



Cannon and Free worked independently, the 

 Soil former at the Desert Laboratory, Tucson, Ari- 



Aeration zona, and the latter at the Coastal Laboratory, 



Carmel, Cal. 



Different plant roots behave differently with respect to effect of com- 

 position of soil atmosphere. Pure carbon dioxide inhibits growth of 

 both Prosopis and Opuntia, but Prosopis stands more carbon dioxide 

 and can get along with less oxygen than Opuntia. Salix was grown 

 entirely without oxygen for 10 weeks without injurious results. 



The presence of living matter in the soil, such as bacteria, protozoa, 

 and fungi, tends to lower the oxygen content and raise the Co^ content 

 as compared with the general atmosphere. This tendency is counter- 

 acted by diffusion between soil and general atmosphere, but the action 

 is slow. 



The authors think the composition of soil atmosphere is an important 

 factor in determining the distribution of plants. Cacti do not grow well 

 in soils heavily charged with Coo. The distribution of Prosopis, Ner- 

 cium, and Salix indicates that the presence of large amounts of Coo is 

 not a limiting factor with them. 



Soil aeration is believed to play an important part in zonation in the 

 central flats, or "playas," in basins of the semi-arid regions. The flats 

 are usuall}- composed of fine soils and are poorly aerated. The vegeta- 

 tion in such flats is often limited or wanting, and around the flats, or 

 "playas," it is arranged in well-defined zones. This arrangement is 

 believed in many instances due not to dift'erences in moisture, but 

 differences in soil aeration. 



The Ecological Significance of Soil Beration. Science, Februarj' 23, 1917. 



SILXTCULTURE, PROTECTION, AND EXTENSION 



Moreillon gives an account of damage done to 



Ati old oak trees in the foothills of the Jura Moun- 



Oak tains by a fungus, Diaporta faleola Tul., which 



Parasite causes droppings of branchlets and twigs, like the 



noted droppings of Norway spruce and other 



species. The droppings take place in the latter half of September and 



