iqiq] waterman— root SYSTEMS 29 



tion in the different layers of the root, and (2) that the distances of 

 these zones from the root tip are specific. Specialized types are 

 also reported: "contractile'' (Rimbach 30); "deciduous"' and 

 "rudimentary" (Cannon 6). Root systems are classified as 

 "intensive" and "extensive" by Busgen (4), and he regards these 

 as hydrophytic and xerophytic, respectively. 



Extension. — The largest amount of agricultural work has 

 been done by King (23), Ten Eyck (39), Shepherd (36), and Goff 

 (18). Their conclusions were largely along practical lines and in 

 many cases simply confirmed conclusions already reached b\' empiri- 

 cal methods. Schulze's (34) work is especially to be commended 

 for carefulness of records and character of photographs. C.\nnon 

 (6, 9) has done the most comprehensive work on arid regions. His 

 records are very complete, but his method of recording is not uni- 

 form and no scales were photographed with his plants. In several 

 cases photographs manifestly of different enlargement were included 

 in the same plate. On other wild herbs the best work was by 

 Weaver (45) on about 20 species of prairie plants. The observa- 

 tions were carefully made and well recorded, and the plants were 

 photographed with scales attached. This work promises well for 

 his "Ecology of roots" (46), soon to be published by the Carnegie 

 Institution. This latter study was undertaken to determine the 

 root habits of dominant and subdominant plants that were growing 

 under a wide range of climatic and edaphic conditions; to find 

 the root relations of the plant communities as units of vegetation; 

 and to determine the root distribution and root competition of the 

 individual species in their relation to other species in the \-egeta- 

 tional group. Other aims were to determine the relation between 

 the root habits of plants in various communities and their succes- 

 sional sequence; and to obtain a more definite knowledge of the 

 indicator value and significance of various species used in classifying 

 lands for grazing or for agriculture ; as well as to aid the forester in 

 selecting sites for afforestation or reforestation. The investigation 

 extended over 4 years, during which time more than 1 1 50 indi\-idual 

 root systems of about 160 species of shrubs, grasses, and non-grassy 

 herbs were excavated and studied on the prairies of eastern Nebraska, 

 the chaparral of southeastern Nebraska, prairies of southeastern 



