ECADS. 



ROOT MODIFICATIONS OF POLYDEMICS. 



Of the 10 polydemic species here described, each growing in at least 

 two different habitats, 7 show very striking changes in their root habits, 

 2 made practically no change, while 1 exhibited only moderate differ- 

 ences of root development. 



Bouteloua, Stipa, and Chrysopsis growing in the plains soil were all 

 deep-rooted species, the latter indeed reaching a depth of over 13 feet. 

 In the sandhills they all conformed to the typical root habit of most 

 plants of this habitat. None of them reached more than half their 

 former depth, but the shallow lateral root development and lateral 

 spread were much more pronounced, especially in Chrysopsis. On the 

 other hand, the more stable species as regards root development, 

 Allionia linearis and Ahronia fragrans, when growing in these same 

 habitats, were only sUghtly or not at all modified. The former showed 

 practically no difference in the sandhill and plains ecads; the latter 

 had a tendency to develop more and longer branches in the sand. 

 These, with Kwleria, which was examined under four distinct sets of 

 conditions in widely separated areas and found to be practically the 

 same in all, form a very conservative group as regards root type, 

 although, as shown by E. Clements (1905), the aerial parts of some are 

 very plastic. This forms a unique problem for further investigation. 



Euphorbia and Yucca, while conforming to the plains root habit 

 in having a rather deep and widely spreading absorbing system, were 

 found to be profoundly modified when grown in the half-gravel. In 

 the former the depth of penetration was always much less, while the 

 branching, like that of Yucca, was much more pronounced. 



Of the three species, Smilacina stellata, Elymus triticoides, and 

 Chamoenerium angustifolium, examined in gravel-slide or half-gravel- 

 slide and in the forest, all took on the typical root habit characteristic 

 of the several habitats respectively. All had fewer branches, a smaller 

 lateral spread, and a lesser depth of penetration in the forest than in the 

 open. The rather great root depth of Chamcenerium in the Douglas 

 fir forest is an exception. This is somewhat puzzling and seems to be 

 quite contrary to the usual rule of root development. 



