2 



PREFATORY NOTK. 



many ways unlimited, surely there could be but one choice as to what 

 his task should be. 



Nevertheless, it is npt in the least the intention to deny to the liter- 

 ature a debt which is plain, but the obligation to some of the more 

 recent "systematic" literature must be said to be dubious when one 

 remembers the paucity of monographic work and contrasts the long 

 list of "new species." It is not too much to say that a considerable 

 proportion of these " new species " consists of isolated descriptions, 

 that there is a lack of coordination with species already known, and 

 that as to many of them even their nearest relatives are not acknowl- 

 edged. It has not been possible to investigate all such. Some are 

 obviously to be rejected — in any event they have not been included 

 here by merit of publication merely. Many others, on the contrary, 

 it has been possible to study more or less fully; of these a surprising 

 number reveal most excellent characters which are not in the least 

 suggested in their often unsatisfactory diagnoses. 



Supplementing the account of structures the student will find 

 numerous records of physiological peculiarities of various species, 

 details of habit or of aspect— features which lure the eye of the expert 

 in the field but which are obscured or lost in the dried specimen. 

 Observations of this character have been eagerly sought, as well as 

 notes concerning associated species, modes of vegetative reproduction, 

 behavior in the dry season and similar data. 



Another well defined aim has been held constantly in view as the 

 work progressed. It was deemed to be in the highest degree desira- 

 ble, on account of the very interesting and instructive variation 

 which exists among Californian plants, that the flora should, in so far 

 as possible, reflect something of this phenomenon. In many cases, 

 indeed whenever opportunity offered, detailed accounts of marked 

 variations have been recorded in the field. Distinctions between 

 variable and invariable types have been rendered far easier of analysis 

 and made in a great degree more certain by a close study of fresh 

 material, which has not infrequently been available in large quantity. 

 Variation ascribable to difference in soil, exposure, dryness and so on 

 is often noted and varieties are here described which may properly be 

 called ecological varieties. 



A very great amount of time and effort has been expended upon 

 the construction of keys; a general key to the families, keys to the 

 genera under the families, keys to the species under the genera, 

 and in some cases even keys to the varieties. The key to the 

 families is a wholly artificial key; it is not intended in the least 

 to indicate natural relationships, but simply to guide the stu- 

 dent, by a path as direct and as sure as possible, to the family. 

 Hence no exceptions are allowed. Since there are, of course, excep- 

 tions in a great many families, genera or even species of the same 

 family may be divided in the key. Moreover, the keys apply only to 

 the species listed. While the specific keys have been carefully made, 

 nevertheless, this is the first descriptive flora in "Western America to 

 present such keys and the student should use them to secure a 



