502 CALIFORNIA ACADEMY OF SCIENCES. 



of settlers for over twenty years, it was possible up to 1872 

 to finci many species during a few hours' search in the 

 moister and least cultivated spots west of the city, some- 

 times in quite large colonies, and yet hundreds of collectors 

 were constantly picking them up. It is indeed astonishing 

 that any specjes survived so long the numerous extermina- 

 ting influences around them ; but the fact shows what per- 

 sistency they possess wherever the slight moisture from 

 summer fogs assists in retaining their vitality, and above 

 all has probably for ages prevented those desolating fires 

 that killed everything where more luxuriant vegetation 

 covers the soil, and hot dry summers cause fires to rage. 

 For it is not only human destructiveness, or hunters' fires 

 that do the damage, as friction of two dry brandies by a 

 gentle breeze, and even the sun's heat, magnified by pass- 

 ing through natural lenses of resinous gums, are believed to 

 be among the causes of fires, even where lightning- is scarce, 

 and inflammable vapors may not be ignited by the sun. 



That the great number found was not merely due to the 

 many collectors at work, is shown by the scarcity of all the 

 species in any similar extent of land in the neighboring 

 counties; for while all those of the counties southward have 

 been reported to be found except ten, we find added Nos. 

 15, 16, 18, 20, 24, which, with 1, 3, 5, 11, 12, 17, 19, 

 20, 21, 25, 26, 30, 31, 41, 42, 43, make twenty-one forms 

 known in the county, to twenty-three in the three large 

 counties next southward, and for the whole region west of 

 San Francisco Bay a total of twenty-nine; while Nos. 14, 

 34, 37, 38, 39, 44, 45, are found only farther south, and 

 Nos. 2, 7, 8, 14, 22 ?, 23, 28, 36, 37, 44, 45, occur on 

 the east but not the west side of the bay. Of tliese,Nos. 

 7, 8, 14?, 28, 37, 44, 45, may be considered regional varia- 

 tions, due to climatic influences of analogous forms found 

 on the west side, or, more strictly stated, the west side 

 forms have varied from previously existing eastern forms. 



There is a possibility that cultivation and preservation of 



