2 Univcrsilj/ of Califnniid I'lihlications in Botany [Vol.7 



]iorkeloy and Oakland Hills lias, by reason of its accessibility, received 

 principal attention. Exten.sive .studies liave, however, been carried 

 on to the north in .\apa Valley (Napa County), in Southern ]\lendo- 

 cino County and in ^Tarin County. To the south certain stations 

 in Monlcicy ('onnty. Santa Cruz County and San ]\Iateo County have 

 received atti'ution and ratluT thorough study. Our own field studies 

 have Ironi time to time been supplemented by examination of plants 

 sent in by a considerable number of correspondents. Collections by 

 the hit t IT have added Sonoma County to the above list and have 

 furnished valuable comparative material from stations in the .same 

 general regions from which our own collections have come. Beyond 

 the range indicated above, some study has been made at stations near 

 Dutch Flat. I'lacer County (3500 ft.) and at Crockers, Tuolumne 

 County (4500 ft.). 



Two seasons, a dry and a wet season, comprise the range of 

 climatic conditions peculiar to that portion of California with which 

 we here are dealing. In general the month of January, which includes 

 the period of greatest precipitation, is the coldest, whereas during 

 August, the driest month, highest temperature conditions usually 

 prevail. The two tables below, Table 1 for San Francisco and Table 2 

 for Berkeley, give the approximate average rainfall in inches month 

 by month in the region surrounding San Francisco Bay. As may 



be noted in the above ta])l('s, approximately three-fourths of the annual 

 rainfall occurs in the months from December to March inclusive. 

 The figures for July and August refer to heavy mists and slight July 

 rains, which sometimes occur. Precipitation in practically all cases 

 consists of storms of one to thirty or more days' duration, interspersed 

 with periods of clear, dry weather. Precipitation in spring decreases 

 as the storms become shorter and less severe and the intervening 

 periods of clear weather increase in length. In the northern part 

 of California the rainfall is much heavier than in the central part, 

 and very appreciable precipitation may occur in July. Such con- 

 ditions are also characteristic of the Sierra Nevada. In Southern 



