292 CARNEGIE INSTITUTION OF WASHINGTON. 



The character and location of the root systems were found to be 

 correlated with the water-content in nearly all cases. In the gravel 

 slide and forest, where the maximum water-content is in the first 12 to 

 18 inches of soil, root systems are uniformly shallow. The plants in the 

 half-gravel slide are somewhat more deeply rooted, probably owing to 

 the greater competition. The sandhills resemble the gravel slide in 

 having a sand mulch of 2 to 3 inches which keeps the soil moist in the 

 upper laj^er. As a consequence, the roots of sandhill species spread 

 widely in the first foot or two and many of them are relatively shallow. 

 The plains and prairies are much alike in regard to root behavior, the 

 chief difference being that the roots of plains species spread laterally 

 to a much larger degree, while those of the prairie species go more 

 directly downward. Maximum penetration was recorded for the 

 prairie, in which Kuhnia and Lygodesmia reach depths of 18 to 20 feet, 

 and Rosa of 22 feet. The great majority of the roots are highly plastic, 

 as is shown by those of ecads especially, but some species, such as 

 Kceleria cristata and Allionia linearis, possess very stable root systems. 

 In determining the competitive relations of plant roots in the same 

 community, use has been made of the quadrat-bisect described else- 

 where. The detailed study of roots was begun in Washington and 

 Idaho in 1914, and a resume of these results is also given in the pro- 

 posed monograph on root systems. 



Reciprocal Transplants, hy F. E. Clements and H. M. Hall. 



A new method has been devised for transplanting related species 

 and ecads to determine the effect of a change of habitat in causing 

 adaptation and variation and in producing new forms. In the earlier 

 work at the Alpine Laboratory species were merely transferred to 

 habitats of measured values and the adaptations correlated with the 

 factors. In the present method the essential feature is the reciprocal 

 planting. This is based upon the presence of paired species or a species 

 and its ecads in neighboring habitats. It is best illustrated in the 

 case of Geranium and Erigeron. Geranium ccespitosum and G. rich- 

 ardsonii are respectively xerophytic and mesophytic minor species 

 or varieties of the same specific stock. Likewise, Erigeron glabellus is 

 the shade form and E. macranthus the sun form or variety of the same 

 species. In reciprocal transplanting, the plants of each variety are 

 not merely transferred to the other habitat, but each plant of Gera- 

 nium ccespitosum, for example, is placed in the hole left by the removal 

 of a plant of G. richardsonii. This insures an exact reversal of con- 

 ditions and permits a clear-cut demonstration of the extent to which 

 the varieties are reversible as well as plastic. For the sake of detailed 

 correlation, determinations of water-content, light intensity, and air 

 and soil temperatures are made at occasional intervals after the plants 

 are fully established. This is naturally during the following year 



