lO ROOT HABITS OF DESERT PLANTS. 



the terms xerophyte and hydrophyte denote more than intensive and exten- 

 sive, as von Alten points out, and from a physiological standpoint, the 

 latter terms are more useful. 



How susceptible to modification, through a variation in the soil medium 

 or its water content, the two classes of roots may be, has not yet been 

 determined. It is believed, however, that the conservative inheritance 

 tendencies are more powerful here than the influence of changing environ- 

 ment, and that the types will remain essentially constant under whatever 

 condition they may be found. 



Among plants with intensive form of root-system are : Mentha piperita, 

 Digitalis purpurea, Artemisia vulgaris, Imperatoria ostruthium. Plants hav- 

 ing the extensive form of root-systems include : Helleborus purpurascens, 

 Solidago canadensis, 'Poly soma integrifolium, Valeriana officinalis. Arnica 

 chaniisonis, Ranunculus acer, Adonis vernalis, and others. 



SCOPE OF THE STUDY AND METHODS. 



When it was proposed some time ago to take up the study of the roots of 

 desert plants, the work was laid down on broad physiological-ecological 

 grounds, and it was realized that as an introduction to such studies, which 

 would be in the nature of things mainly experimental, a knowledge of the 

 habits of annuals and of perennials afield was a prerequisite. As an exact 

 description of the root-systems of the most characteristic forms was wanting, 

 the prosaic task of excavating roots was undertaken, and the present paper 

 includes an account of the results of this work. 



While the plants selected for study have been such as are presumably 

 representative of all types, they do not include many which would be of 

 interest, but an account of which would in a degree duplicate results already 

 attained. Aside from the usefulness of the bare descriptions of root- 

 systems in later experimental work, they will probably be found of value 

 in comparative root studies, where the root-systems of other arid regions, 

 in which the physical conditions are otherwise different from those of the 

 Southwest, are carefully worked up and mapped. Much interest has been 

 found in comparing the nature of the root-systems and their variability as 

 observed in the field with the leading and obvious characters of the environ- 

 ment, and it has been found, as will be related later, that in certain instances 

 there is a very clear relation between root type and plant distribution, as 

 well as between root type and other habits of the plant. The root-systems, 

 therefore, have been studied only in the field, and natural conditions h, ve 

 uniformly been described. 



In the course of the research different methods have been developed to 

 suit the particular form of roots studied. In the case of annuals, the entire 

 root-S3'stem, or as much of it as could be removed from the ground, was 

 measured and photographed, the photographs being somewhat under life 

 size. 



