REVIEWS 307 



chapters were added on the heart rot caused by Fomes annosus, a 

 root rot that is very prevalent in England and on the Continent; a 

 short chapter dealing with the heart-rot fungi Polyporus schweinitzii, 

 Poria vaporaria, Polyporus sulphiireus, and Trametes pini; a rather 

 extensive chapter on Armillaria mellea, and a brief concluding chapter 

 on various leaf and seedling diseases. The author reviews the litera- 

 ture in each instance, describes the disease, and gives a detailed 

 account of the causal organism, its mode of action, reproduction, 

 infection, etc., the factors that contribute to its activity, and the 

 approved methods of prevention. The illustrations are well-chosen 

 and well-executed. The amount of new materials presented is pro- 

 portionately small, but from a pedagogical point of view this little 

 volume is of very great excellence. It is a book which foresters and 

 students of forest pathology will read with fascinated interest. 



J. H. F. 



Root Development in the Grassland Formation: A Correlation of 

 the Root Systems of Native Vegetation and Crop Plants. By John E. 

 Weaver, Carnegie Institution of Washington. Publication 292. Pp. 

 151, 39 text figures and 25 plates of which two are colored. 



This is the companion volume to "Ecological Relations of Roots" by 

 the same author reviewed by Dr. Toumey in the Journal of Forestry, 

 17:990-993, 1919. Since the publication of the latter, the author has 

 extended his investigations to more than twenty-five stations in the 

 grassland associations of Kansas, Colorado, South Dakota, and 

 Nebraska. More than 1.500 root systems were examined and for prac- 

 tically all of the species, the root systems were excavated almost in 

 their entirety, including thirty-eight new root systems of important 

 species of the prairie, sandhills, and plains and more than eighty exam- 

 inations of the root systems of crop plants in widely varying soil types 

 and conditions of growth. 



These studies revealed marked differences, either in the lateral 

 spread of roots, depth of penetration, or output of branches. These 

 changes were in most cases correlated with changes in the water 

 content of the soil. A close correlation between depth of root pene- 

 tration and efficient rainfall was noted. Soil texture was found to 

 exert a direct influence upon root development through water content 

 and aeration. Variations in behavior appeared to be responses to dif- 



