McKenney, Notes on Plant Distribution in Southern California. 173 



Salix lasiolepis Benth., S. laevigata Bebb., Baccharis viminea DC. 

 and Nicotiana glauca Graham. The first three speciea, in external 

 features are very much alike. This resemblance h so striking 

 tbat Baccharis, although a typical composite, is often called by 

 Californious, „the flowering willow". An equal admixture of Salix 

 and Baccharis is shown in Fig. 5. 



During the wet season herbs are uncommon and are restricted 

 to the borders of the river beds. After the flow of water ceases, 

 which is usually in April, raany of the herbs form the Mesa spread 

 over the river beds. Throughout the year, however, the four 

 mentioned shrubs constitute the central feature and enable one to 

 distinguish the river beds at considerable distances. 



Mesa Formation: This formation is characterized by an 

 •absence ot all arborescent and shrubby growth. Although the 

 Vegetation is herbaceous, grasses are uncommon and form an in- 

 signiticant part of the floia. The Vegetation is of two types, a 

 more or less succulent form and a hard dry form with a withered 

 appearance. The leaves of the first type are proportionally much 

 larger than in the second type. In the latter, there is a tendency 

 to spine development. The principal species are: Datura mete- 

 loides DC, Suaeda Torryana Wats., Salicornia ambigua Michx., 

 Mesembryanthemum crystallinum L., Sesuvium portulacasfrum L., 

 Eremocarpus setigerus Beuth., Sarcobatus Maximiliana }^ees, Asclepias 

 eriocarpa Benth., Ätriplex patula L., A. californica Moq., Helio- 

 tropium curassavicum L., Euphorbia albo-marginata T. et G., 

 Croton tennis Wats., Grindelia robusta Nutt., Centanrea militensis L., 

 Cucurbita foetidissima H. B. K., Malva borealis Wallm., Helianihus 

 annnus L., Heterotheca grandiflora Nutt., Erigeron canadensis L., 

 Chenopodium ambrosioides L., Eurotia lanata Moq., Trichostema 

 lanceolatum Benth., Hemizonia fasciculata T. et G. var. ramosissima 

 Gray, Nemocaulis Nuttallii Benth., Fterostegia drymarioides F. et M., 

 Lastarriaea chilensis Remy and Eriogonum Thurberi Torr. The 

 first and last six represent the more extreme forms, while the 

 remainder are more or less intermediate in character. 



The more succulent form are commoner on the more alkaline 

 sections of the Mesa and the others on the less alkaline sections. 

 Both types tend to assume a spreading habit. Histological diffe- 

 rences must be reserved for discussion in a later paper. In the 

 succulent forms, when present, the leaves are fairly large; in the 

 other form the leaves are small and in many cases almost reduced 

 to small spines. 



Bog Formation: This formation, is devisable into two types; 

 namely that having surface water continually and that only having 

 the ground saturated with water. The forms found in first type 

 are in most cases abundant in such formations. They are: Typha 

 latifolia L., T. angustifolia L., Azolla filiculoides Ehrh., Scirpus 

 lacustris L. var. occidentalis Wats., Lemna minor L., Nasturtium 

 oßcinale R. Br., Hydrocotyle ranunculoides L. fil., Mimulus luteus 

 L. and Urtica holosericea Nutt. The last two are not so com- 

 monly lound in bog formation. 



