ROOT-SYSTEMS OF PERENNIALS. 



The problem of studying the roots of the larger plants in the field, and of 

 recording the results, is naturally quite different from that of examining the 

 root-systems of annuals. The environment to which the roots of perennials 

 are exposed and to which they should be related, is likewise much more 

 varied than that of the smaller plants of briefer life span. In the case of 

 the annuals the entire root-system might by appropriate means be brought 

 under the eye, photographed, measured, and examined microscopically; but 

 such procedure is impracticable in perennials, and choice had to be made 

 arbitrarily between minute examination of ultimate roots, as Biisgen studied 

 the roots of Javanese and German trees, and a study of the more permanent 

 portions of the root-systems. Since the survival means successful resistance 

 to desert conditions, and, further, as the study was primarily one in which 

 the plant was to be compared to its environment, the latter method was 

 decided on. 



Accordingly, in this report on the results of the investigation, the mature 

 root-systems are characterized and the more obvious relations to tempera- 

 ture and water are presented. 



The perennials selected for study comprise the most striking ones only, 

 and probably do not include many which will be found worthy of subsequent 

 examination. The list includes trees and shrubs, mainly the latter, and 

 among these is a great diversity in habits and habitats. There are fleshy 

 as well as non-fleshy forms; plants with shallow and those with deeply 

 placed roots ; plants deciduous as well as evergreen ; those which come into 

 leaf in summer only and those which form leaves whenever there is adequate 

 amount of water whatever may be the time of the year, and finally there 

 is one parasite (Krameria). 



Following is a list of the species examined, together with the habitats in 

 which they were studied : 



TuMAMOC Hill: Echinocacius wislizetii Engelm., Encelia fariiwsa Gray, Jairopha carJio- 



phyila (Torr.) Muell. Arg., Opnntia discata Griffiths, Opuntia Icptocaulis DC, 



Opuntia versicolor Engelm. 

 The Bajada: Camegiea gigantea (Engelm.) Britt. and Rose, Covilica iridentata (DC) 



Vail, Fouquieria splendens Engelm., Franseria deltoidea Torr., Krameria 



canescens Gray, Krameria glandulosa Rose, Opuntia arbuscula (?) Engelm., 



Opuntia fulgida Engelm., Riddellia cooperi Gray. 

 The Bajada, Rincon Mountains: Dasylirion texanum vScheele, Mortonia scabnlla 



Gray, Yucca sp.. Yucca radiosa Engelm. 

 Flood-Plain of Santa Cruz and West Wash: Condalia spathidafa Gray, Ephedra 



irifurca Torr., Koerberlinia spinosa Zucc, Opuntia vivipara Rose, Zizyphus 



parryi Torr. 



Besides these forms some observations were made also on Prosopis 

 velutina Wooton, Lycium sp., Olneya tesota Gray, Parkinsonia microphylla 

 Torr., and a few other forms which will be given incidentally in the account 

 of the root-systems below. 



