8 DESCRIPTIVE FLORAS FOR CALIFORNIA, 1838-1880 



80 may bo used to compare or contrast related species. Since species in great part tend to occupy 

 climatically different areas, knowledge of the climate or climatic position is sometimes effective 

 in relating dubious plant forms to their proper groups. 



7. Record of the altitude at which material is taken is always important since it is of pri- 

 mary use in the determination of zonal values. 



8. Studies of the associated species at a given locality or in a natural area, their character, 

 abundance and habits, yield basic material of great importance in the segregation and correlation 

 of natural units, especially if the determinations are made in connection with a consideration of 

 climatic or edaphic factors. 



9. Determination of the limits of geographic range of a species is always of great impor- 

 tance and the collection of material must keep this object in view. No two species have exactly 

 the same range, because each species by its constitution reacts in its own peculiar way to environ- 

 mental conditions. 



10. Determination of the center or area of highest development of a species by the tests of 

 abundance or dominance of individuals, their size, vigor, tolerance and fertility ; by the degree 

 and uniformity of morphological differentiation; by the capacity to hold the territory in com- 

 petition with other species as involved by temperature, water, insolation, fire and other influences: 

 consideration of these factors must be regarded as a necessary preliminary to the satisfactory 

 description of a species for use in a flora which designs to portray the plant cover of a country. 

 In presenting a record of the plant populations it is necessary that descriptions be written so as 

 to give a view of the prevailing or biologically successful form of a given species, the biotype or 

 natural unit, so to say, instead of the artificial "type" of the herbarium which may represent an 

 outlying or unusual form. 



11. Seasonal changes in the structure of organs on one individual, or the production by the 

 individual successively of morphologically different forms of one organ, have a weighty signifi- 

 cance on account of the fact that such expressions are often described as distinct species. 



12. The degree and character of morphological variation of organs in a species as expressed 

 by a single individual or by several phenotypic individuals from one habitat, or by a colony ob- 

 viously to be accepted as of one genetic constitution, form a subject for useful field study, and 

 if validated by records and specimens have a marked value in the work of defining the limits of 

 species. 



13. Senilism or lethalism in the plant are phases which may likewise yield evidence of value 

 bearing upon the special morphology of a group or the enigmas of relationship. 



Ample field records must be made in field books always carried on one's per- 

 son, so that notes may be made on the spot. Such practice becomes by habit a prime 

 duty in the field. Collections should always be serially numbered in sequence as 

 gathered. Field books thus enriched day by day provide a source of wealth in the 

 laboratory and herbarium for which there is no substitute. Photographic records 

 in the field are also a source of great profit in scientific studies. 



Herbarium, laboratory and bibliographic research and garden cultures have 

 each in a flora plan a markedly cogent place, but the purpose of the present note 

 is to evaluate field activity. On account of the extreme diversities of climate and 

 topography in California, the native vegetation presents markedly peculiar, not 

 to say singular, features. Field investigation of the native plants is, therefore, in 

 this undertaking heavily weighted by its fruitf ulness and inspiring values. To this 

 day entirely new plants with as strongly marked characters as any obtained one 

 hundred years ago are being found in California. These are highly restricted 

 species of micro-climatic pockets, and not merely segregates of old or well-known 

 species. These discoveries emphasize tlie aspects of geographically narrow species, 

 which has to do with problems of great moment. With an appreciation of local- 

 ized endemism and its biological significance, as well as of wide-spread species and 

 broad influences, there may thus be related the essentials preliminary to an under- 

 standing of the very beginnings of knowledge concerning the origin of the varied 

 floras of California. 



Willis Linn Jepson. 

 University of California, 

 Berkeley, 

 April 25, 1927. 



