122 Botany 



No. 286. WEAVER, JOHN E. The Ecological Relations of Roots. Octavo, 128 pages, 

 33 plates, 58 figs. Published 1919. Price $3.00. 



The root habits of dominant and subdominant plants growing under a wide 

 range of climatic and edaphic conditions are given. These data are taken from 

 the examination of over 1,150 root systems of about 140 species of shrubs, grasses, 

 and other herbs. The communities studied were the prairies of eastern Nebraska, 

 the chaparral of southeastern Nebraska, the prairies of southeastern Washington, 

 the plains association and sandhill subclimax of Colorado, and a successional series 

 including the gravel-slide, half-gravel-slide, and forest communities of the Rocky 

 Mountains of Colorado. The general characters of the root system of a species 

 are often as marked and distinctive as are those of the above-ground vegetative 

 portions. Moreover plants growing under different climatic and edaphic condi- 

 tions e. g. prairie, sandhills, forest have root habits which, although showing 

 great individual variation, are often similar in their more general aspects. This 

 has been designated the community root habit. Prairie plants are mostly deep- 

 rooted, about 60 per cent reaching depths ranging from 4 to 20 feet. They em- 

 phasize depth of penetration and a wide spreading of root branches, but not in 

 the surface soil. Plains species are likewise deep rooted but exhibit a pro- 

 nounced development of surface absorbing and widely spreading laterals. Sand- 

 hills species were rooted more superficially and showed as a community an even 

 more conspicuous surface absorbing system. Thus community root habits were 

 determined for the other major units of the vegetation studied. The root systems 

 of a number of species growing in two or more distinctly different habitats 

 were usually found to take on the root habit characteristic of the community as 

 a whole, although certain stable species modified their root habits but little. 

 Root habit was correlated with environmental conditions, particularly with the 

 evaporating power of the air and the water-content of the soil. 



A knowledge of the position and competition of roots is indispensable in ex- 

 plaining the phenomena of succession. Since root position so clearly reflects 

 the moisture conditions of the soil, especially when interpreted in its community 

 relations, a study of the root habits of plants greatly increases our knowledge of 

 the value of various plants in indicating lands of agricultural or non-agricultural 

 value. A knowledge of root habits is of further value in solving the problems 

 of the competition of range species and the improvement of the range. Finally, 

 root systems indicate the distribution of soil moisture in various habitats, and 

 thus should aid the forester in selecting sites for reforestation or afforestation. 



No. 206. JOHNSON, DUNCAN S., and HARLAN H. YORK. The Relation of Plants 

 to Tide Levels: A Study of Factors affecting the Distribution of 

 Marine Plants. Octavo, 162 pages, 24 plates, 5 text figures. Pub- 

 lished 1915. Price $2.50. 



The vertical and horizontal distributions of some 200 species of plants growing 

 in and about the Inner Harbor at Cold Spring Harbor, Long Island, New York, 

 and the factors determining these have been carefully studied. The tidal changes 

 in water-level for all shore habitats have been accurately measured. The dependent 

 or associated changes in other factors affecting plant distribution have been either 

 measured or estimated and their relative effects analyzed. The distribution of 

 most shore plants in relation to tidal submergence and exposure is much more 

 precisely limited than is indicated by the terms, "between tide marks," "near low- 

 water mark," etc., commonly used to indicate the distribution of littoral organisms. 

 An adequately exact definition is given for the variously used term "littoral." The 

 chief vegetational zones distinguished, with their upper and lower limits, reckoned 

 from mean low-water, are: (1) Plankton of diatoms and Peridinese. (2) The 

 bottom vegetation ( 5 to + 1.5 feet) of algae, Zostera and Ruppia. (3) The 

 very sharply marked mid-littoral belt (1.5 to 6.5 feet) including a Spartina glabra 

 'association on beaches and marshes and a rockweed association on the wharves. 

 (4) The upper littoral belt (6.5 to 8 feet) with quite varied vegetation of algae, 

 dicotyledons, and monocotyledons. (5) The supra-littoral belt (8 to 12 feet) with 



