4 CONTENTS. 



Root Habits of Desert Plants — Continued. 



Winter Annuals — Continued. page. 



Monolepis chenopodioides 36 



Orthocarpus purpurascens 36 



Parietaria delailis 38 



Phacelia tanacetifolia 38 



Plantago fastigiata 38 



Rafinesquia neo-mexicana 39 



Streptanthus arizonicus, Sisymbrium canescens, Sisymbrium reflexum . 39 



General Conclusions and Summary of Studies on Annuals 40 



Root Systems of Perennials 43 



Plants from Tumamoc Hill 44 



Echinocactus wislizeni 44 



Encelia farinosa 46 



Opuntia discata 48 



Opuntia leptocaulis 50 



Opuntia versicolor 52 



The Bajada 55 



Carnegiea gigantea 55 



Covillea tridentata 58 



Fouquieria splendens 61 



Franseria deltoidea 64 



Krameria canescens 67 



Opuntia arbuscula 69 



Opuntia fulgida 71 



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 



