4 CONTENTS. 



Root Habits of Desert Plants — Continued. 



Winter Annuals — Continued. pace. 



Moni)Ic|)is chcnopodioides 3^ 



Orlhocarpus purpurascens 3^ 



Parietaria dcbilis 3^ 



Phacelia tanacctifolia 3^ 



Plantago fastijjiata 3^ 



Rallmsiiuia nco-iiiexicana 39 



Strci)lantluis arizonicus, Sisymbrium canescens, Sisymbrium reflexum . 39 



General Conclusions and vSummary of Studies on Annuals 40 



Root Systems of Perennials 43 



Plants from Tunianioc Hill 44 



licliinocaclus wislizeni 44 



Encelia farinosa 4^ 



Opuntia discata 4^ 



Opuntia Icptocaulis So 



Opuntia versicolor 52 



The Bajada 55 



Carnegiea gigantea 55 



Covillca tridentata 58 



Foutiuieria splendens 61 



Franseria deltoidea 64 



Krameria canescens 67 



Opuntia arbuscula 69 



Opuntia fulgida 7i 



Riddellia cooperi 73 



Dasylirion texanum, Yucca radiosa, Yucca sp., and Agave sp 75 



The Flood-plain 78 



The Flood-plain of the Santa Cruz 78 



Koerberlinia spinosa 78 



Prosopis velutina 80 



Condalia spathulata and Zizyphus parryi 81 



Ephedra trifurca 82 



Opuntia vivipara 83 



Experimental Cultures 84 



Physiological Features of Root-Systems 87 



"Character' ' in Roots 87 



The Relation of Roots to Soil Temperature 88 



The Relation of Roots to Water 89 



Relations of the Roots of Neighboring Plants 92 



Root Habits and Plant Distribution 94 



Summary 95 



