MOVEMENTS OF VEGETATION IN THE SALTON SINK. 123 



of this volume by Professor Blake. The relative rates of evaporation by months are : Jan- 

 uary 10, February 10, March 18, April 20, May 26, June 34, July 30, August 28, September 

 23, October 21, November 12, December 9 (see also p. 134 for evaporation of 1909-10). 



That the bareness of the soil laid dry in midsummer was due to desiccation and not 

 to dearth of available seeds was made evident by the fact that below this arid belt was a 

 second zone of Atriplex which appeared to occupy a strip uncovered during the autumnal 

 months. It is a notable fact, however, that the formation of two definite bands or zones 

 did not occur in any succeeding year, although there were a few late-summer germinations 

 even as late as 1912, at which time the original invasions of 1906 and 1907 were still recog- 

 nizable. The pelicans and cormorants were frequently observed standing on the shore 

 near the margin of the water, during the middle of the summer especially, and there seems 

 to be greater probability of their agency in bringing seeds to the summer zones than to 

 any other formations examined around the lake. Furthermore, the species represented 

 were those which might most readily have adhered to the legs and feathers of these birds. 



The greater number of plants invading the strands were carried there in the form of 

 seeds by the wind, by flotation, or by birds, as will be discussed somewhat fully in a later 

 section of this paper, but the emersion of 1907 was characterized by some reoccupations 

 of a different character. The waters of the lake rose rapidly to the maximum level in Feb- 

 ruary 1907 and then fell quickly. In many places not particularly subjected to violent 

 wave-action shrubs and small herbaceous plants stood erect in place, although the water 

 about their bases was perhaps a foot in depth. If, as in the case of Atriplex and Suceda, the 

 branches bore mature fruits, many of these might be retained until after the soil about 

 the base of the plant had been bared, when their dispersal by the simple mechanics of the 

 plant would result in some patterns of reseeding independent of other agencies. 



The rapid recession of the water down the gentler slopes was not accompanied by 

 any sorting of material in lines parallel to the periphery of the lake at Mecca or on the 

 Imperial Junction Beach. The only specialization occurring was that by which suspended 

 silt was dropped in the channels of the washes formed previous to the inundation. The 

 recession of the water left these as moist strips of mud a few feet or a few inches in depth, 

 which furnished conditions for Heliotropium, Lepidium, Typha, Rumex, and Leptochloa in 

 a loose formation extending radially to the lake. 



The salt-grass or Distichlis had formed a few mats on the strand laid early in 1907, 

 but these plants were already showing the strain of desiccation, and Leptochloa had also 

 come in at a level corresponding to the autumnal band of Suceda. A number of hard- 

 shelled fruits of Cucurbita palmata had been cast ashore at various places on the slope, but 

 no germinations had been accomplished. 



The observational area near Mecca was upon a slope in which the fall was not more 

 than 1 in 400, and as the surface was uneven, the vegetational reactions were not so easily 

 interpreted. In fact, the limit at which the pitch of a slope may be sufficient to produce 

 banding or zonation of the plants upon the given rate of evaporation may be taken to lie 

 between that of the Mecca and that of Imperial Junction beach. 



The circumnavigation of the lake in February 1907 was begun at a point on this area, 

 a boat being brought up the shallow channel made by the advance of the water up a sunken 

 road. The actual margin of the water at this time was an exceedingly crooked line and 

 the high level of the water might not be accurately laid down except at a few points. The 

 second visit to the place in February 1908 showed that in addition to the survival of a 

 few individuals of Atriplex and Suceda within the inundated area, a few trees of Salix and 

 Populus also endured submergence of their roots for several months. A great number of 

 spreading trees of Prosopis pubescens had been killed and the wood of the trunks and 

 branches had become exceedingly brittle. The total width of the emersed strip here was 

 about 1,400 feet. In addition to the moisture effects from saturation, an uneven underflow 



