22 THE POPULAR SCIENCE MONTHLY 



THE FLORAL FEATURES OF CALIFORNIA 



By Dr. LeROY ABRAMS 



ASSOCIATE PROFESSOR OF BOTANY. STANFORD UNIVERSITY 



SHUT off from eastern North American by the high Sierra wall, that 

 formidable harrier to the eastern and western migration of plant, 

 as well as animal life, and possessing a climate unlike that of any other 

 part of the continent, California has developed a flora that is unique. 

 Indeed, isolation has been so complete that the California flora, with 

 its host of peculiar or endemic species and even genera, displays many 

 qualities characteristic of an insular flora, such as one might expect to 

 find on a remote oceanic island. To the traveler familiar with the flora 

 of the Mississippi Valley or of the Atlantic States, California plants 

 seem as foreign as those of southern Europe. Species of such well- 

 known genera as Quercus. Primus and Rhamnus (the oak, the cherry 

 and the buckthorn) are so unlike their eastern relatives in foliage and 

 general aspect that their true relationship is revealed only on close 

 scrutiny. 



But if the Sierra wall with its snow-clad summits has been an 

 effective barrier to the eastern ami western migration of plants, it has 

 been likewise effective as a pathway for the southern migration of 

 northern plants. And the warm valleys and foothills that lie at its 

 base have been similar pathways for the northern migration of southern 

 types. We find, therefore, the California flora composed of three dis- 

 tinct elements, the Californian, the Boreal, and the Mexican. 



The Californian element, as recently discovered fossils prove, was 

 established before the Glacial Period, and through its preservation from 

 the destructive ice sheet, California has been able to hand down such 

 a priceless heritage as the sequoias, an all hut extinct race that at one 

 time flourished over North America, Europe and Asia, extending as far 

 north as Greenland and Spitzbergen. With the sequoias have come 

 clown many other conifers, making the California coniferous forests the 

 richest in the world. 



The Boreal or northern element, pushed southward by the ice sheet 

 of the Glacial Period, formed a belt on the California mountains below 

 5,000 to 8,000 feet, the perpetual snow line of the ice age. At the end 

 of the period, the ice retreated upward and northward, followed by the 

 boreal plants, with the result that we now have arctic and subarctic 

 species stranded on mountain tops a thousand miles or more south of 

 their general range. 



The Mexican element has migrated, largely since the Glacial Period, 



