DEPARTMENT OF BOTANICAL RESEARCH. 



63 



Of the 144 spermatophytes, 113 are indigenous and 31 are intro- 

 duced. With the exception of a few which have been found on the 

 beaches of Salton Sea, all the introduced plants are confined to those 

 parts of the Sink which have been reclaimed through the economic 

 operations of human settlement; in no case have they been able to 

 intrude where natural conditions remain. 



Of the indigenous species of the Sink, 9 are trees, 22 are shrubs, 

 13 are semishrubs, 23 are perennial herbs, and 46 are annual herbs. 



The indigenous spermatophytes may be divided in accordance 

 with their habital character into two classes: (1) those which grow 

 only in water or in moist soil; (2) those which grow in arid soil. 

 The latter constitute the flora of the absolute desert. Isocoma and 

 the two species of Prosopis are included in the second class, although 

 they grow also in damp soils. 



A floral census evidently conveys an inadequate and incorrect 

 presentation of the phyto-geography of a region, if an equal value is 

 given to those species which are widely distributed and abundant and 

 those which are rare, of which, perhaps, the finding of but a single 

 specimen may have rewarded extensive explorations. With this in 

 view an attempt has been made in the table below to segregate those 

 species which are fairly frequent, at least in some parts of the Sink, 

 from those which are rarely seen. In making such a division the 

 tabulator must needs be guided largely by what he has himself 

 observed, so that his results are subject to the revision of other and 

 more extended investigations. Especially does this apply to the 

 annual herbs; for under the irregular meteorological conditions of the 

 Sink an unusual season may bring up in abundance annuals which in 

 ordinary years make hardly any appearance. But it is believed that, 

 on the whole, those species which are indicated in the table as "fre- 

 quent" are those which the botanist will certainly find, in more or 

 less abundance, not in all but at least in some part of the Sink. 



It appears by the table that of the 72 xerophytes 42 are common 

 in some parts of the Sink. The species which are abundant every- 

 where in the arid soils of the Sink are but two — Atriplex canescens 



