Origin of California Lichen Flora. 219 



to receive stimuli or transmit acquired characters. We have 

 as means of reproduction only a sexually produced fungus 

 spores which germinate mayhap in. the presence of the proper 

 algae, or else bits of the thallus (soredia) blown about to start 

 new lichens when the conditions are right. Yet, in spite of all 

 this there is real evolution among them, and they do have a real 

 heredity, else there could be no definite species. 



Lichens are among the most variable of all organisms 

 and are also among the most widely distributed. Their inherent 

 variability causes them to develop a great variety of forms which 

 intergrade in a multitude of ways. But this inherent variability 

 in the case of individuals containing material from a single 

 parent only, as in lichens as a whole, seems to give rise to few or no 

 new species when the factors of the environment over large areas 

 are relatively unchanging. Hence the comparatively fewer 

 number of unique endemic species in the eastern United States 

 and this in spite of the fact that there seems to be no definite or 

 fixed limits to the variability of lichens. The relative uniform- 

 ity of environment seems to be sufficient to retain the same 

 mean average of development, to restrict the species within 

 certain definite limits. 



It follows, therefore, that when these organisms are suf- 

 ficiently isolated and placed under conditions different from 

 those obtaining in most regions, they are prevented from retain- 

 ing the same m.ean average established in regions where there is 

 no isolation. I believe that the isolated lichens, which are in- 

 herently exceedingly variable organisms, have this variability 

 controlled by a kind of orthoselection, which thus works un- 

 impeded until new species are produced. These new species 

 may become fixed, under the influence of their new environment, 

 in the lapse of ages, or they may be as yet unstable, perhaps not 

 having had sufficient time to become completely fixed. 



As examples of fixed species developed under the influences 

 suggested in this paper, we may cite Caloplaca coralloides, 

 Schizopelte californica, Raynalina reticulata, and Lecanora pinguis. 

 On the other hand we may regard the following quite variable 

 forms as not yet firmly fixed: Lecanora bolanderi, Dendrographa 



