384 .BOTANICAL GAZETTE [November 



practically always represented by at least a few specimens, is 



Psilocarphus hrevissimus, ■ a whitish-headed composite scarcely 



I cm. tall. 



Marginal circum-area 



The marginal zone is characterized in late spring by Deschampsia 

 danthonioides . Sometimes this grass forms an almost pure stand 

 after the disappearance of the meadow-foam, which, it will be 

 remembered, marked the marginal zone in the first part of the 

 season. As would be expected, the marginal zone is subject to 

 invasion from within and from without, but it remains, as a rule, 

 a very definite and distinct entity. 



The inner boundary of the marginal circum-area is sometimes 

 made by a thin line of Achyrachaena mollis, an inconspicuous 

 composite that becomes noticeable in fruit by the spreading out 

 of its silvery pappus. This same narrow line may be marked a 

 little later in the season by a scattered ring of a kind of tarweed, 

 Hemizonia Fitchii. Neither the Achyrachaena nor the tarweed, 

 however, are essential elements in the circum-area; often they are 

 entirely absent. 



The ordinary drained areas of the Sacramento plains have a 

 large proportion of introduced plants, especially grasses, bur clover, 

 and species of Eradium. This is true of abandoned fields and of 

 areas never under cultivation. The depressions, on the contrary, 

 have an almost strictly native vegetation. If a patch of cultivated 

 ground is left untouched, the depressions soon return to their 

 original condition, unless the field has been thoroughly manured 

 and cultivated. This recrudescence of the original vegetation, 

 of course, is readily possible where most of the species are annuals. 

 A definite case of return of native flora was noted in North Sacra- 

 mento. An abandoned field had grown up to European grasses 

 and weeds, but a low place in it, which plainly showed the marks 

 of previous cultivation, was now like any of the primitive untouched 

 adobe depressions. On May 15, 191 7, the vegetation of the central 

 area, about 10 m. across, was chiefly Allocarya and Eryngiiim, 

 with a small amount of Mimulus, Downingia, Gilia leucocephala, 

 and Deschampsia danthonioides. Outside this central part was 

 a wide circum-area dominated at this time by Deschampsia, 



