^74 Botanisches Centralblatt. — Beiheft 3. 



The second type of the formation is characterized ny the 

 following: Stachys hullata Benth., Trifolium involucratum Willd., 

 Apium graveolens L., Cotula coronopifolia L. and the Houttynia 

 <^alifornica B. et H. of the caiions. It may be noted that in this 

 second type we find smaller intercellular Spaces than in plants 

 growing where there is surface water for long periods. 

 fiandy beach is quite bare of Vegetation. However, the rocks of the 



Strand Formation: Between low and high tide marks, the 

 liills which project into the ocean have a large supply of algoid 

 growth in this region. Fucus serrata L., F. fastigiata L., Clado- 

 phora rupestris L., Plumaria elegans Schmitz and Corallina offici- 

 ■nalis Ell. are the most common forms found here. 



Above flood tide, where there is a beach, it is flat and un- 

 broken by dunes. The growth here is almost entirely herbaceous 

 in chai acter. The few woody forms are low and have a spreading 

 habit. Oenothera cheirantliifolia Hörnern, var. sußruticosa Wats. is 

 the common woody form. Other characteristic species are: Abronia 

 Tuaritima Nutt., A. nmbellata Lam., Mesemhryanihemum aequilaterale 

 Haw., Franseria bipinnatißda Nutt. and Calystegia Soldanella L. 

 (Fig. 6.) 



It will be noticed that these forms are quite succulent With 

 the exception ot Franseria, all have a spreading or creeping habit. 

 The Abronias are noteworthy in that, as will be seen in Fig. 6, 

 they have their leaves placed nearly vertically. It will also be 

 Seen that the leaf surfaces face in different directions. In some 

 cases they face east and west and in others north and south. It 

 may be that this position, which appears to be a fixed one, is an 

 ■attempt to obtain rather than to avoid strong light. Were the 

 leaf surfaces placed in a dorso-ventral position, they would shade 

 one another too much as they grow in compact masses. 



Grasses, which constitute an important part of many Strand 

 formations, are here but poorly represented. (Fig. 7.) 



In addition to its own peculiar plants, the Strand formation 

 •contains a number of species which are present in the more alkaline 

 portions of Mesa. The forms common to both formations are: 

 Salicornia ambigua Michx., Sesuvium portulacastruin L., Atriplex 

 californica Moq., Sarcobatus Maximiliana Nees and Meseynbryan- 

 ihemum crystallinum L. When growing on the coast these forms 

 seem less stifF and hard than when growing inland. In Mesembryan- 

 themum crystallinum L. the Strand form has larger and much 

 greener leaves than the inland form. When growing on the 

 alkaline Mesa all parts are colored deep red. 



Conclusion. 



If we would find the causes of distribution we must first 

 ascertain which conditions are alike in all parts and which vary. 

 It rarely happens, that by itself, any one factor is responsible for 

 plant distribution. Usually many factors are operative, although 

 some are much more effective than others. The importance of any 

 one factor is not determined by, what may be called, its absolute 



