176 CALIFORNIA ACADEMY OF SCIENCES. 



species is much elongated, dying after the fruit has 

 ripened. The period of bloom is about six weeks, but 

 many of the species bear flowers at other times. 



The hybrids of Ceanothus are found wherever two 

 species of the same section gi-ow together. As a rule, 

 to which there are, however, many exceptions, no two 

 species of the same section (only two sections are here 

 recognized) occupy the same area. Either one grows at 

 a higher elevation or at a different exposure, and the 

 hybrids occur along the lines of junction. They seem 

 usually to be fertile, and show every gradation from one 

 to the other parent. The only infertile hybrid, within its 

 section, known to me is No. 69, C. incanus x papillosus. 

 In this the ovaries are more or less abortive and no fruit 

 was formed. Of the hybrids between members of the 

 different sections only two are known, C. Ve/'tchianns, 

 which appears to be C. tliyrsiflorus X C . rigidus and 

 C . rugosus, which is C. vcliitiniis X C . ^?'ostratns. 

 Nearly if not quite all the species described from Euro- 

 pean gardens are hybrids of C. American us and C. 

 azureus — most of them artificial. 



Ceanothus is very readily and completely killed by the 

 fires which so frequently run over the chaparral hills of 

 California. About the places where their parents grew 

 the seedlings then spring up in great numbers, although 

 they are otherwise rarely seen. A certain proportion of 

 these seedlings are always, where two different forms 

 have grown intermingled, found to be hybrids. If the 

 district should be again swept by fire before the seed- 

 lings bear fruit the species in that locality would be ex- 

 terminated, with perhaps an occasional sheltered exception, 

 which may almost as readily be a hybrid as one of the 

 parent forms. In this way, as may readily be conceived, 

 a fertile hybrid might become established as the prevail- 



