VOL. 5] Error in Genera and Species. 93 



apparent forgetfulness of the lapse of time involved in geologic 

 periods, which are certainly long enough to quite preclude the 

 possibility of the survival of any species then existing, while it 

 is quite impossible to grant that evolution acting under different 

 environment in widely separate regions will produce identical 

 organisms. Nature works, as has been well said, along lines of 

 least resistance, and certainly the line of least resistance here 

 is the dispersion of seeds by some of the numerous agencies 

 that are known to be competent. As this introduction and 

 interchange of plants has taken place in the past so we find it 

 now, but at a greatly accelerated rate, owing to the much more 

 rapid and frequent intercourse. 



How shall we know whether a plant like Erodium cicutariu m 

 or Bowlesia lobata is indigenous, or not very remotely introduced? 

 By the locality where its variations abound, not by its numerical 

 abundance, for it is a curious fact that Eurasian weeds seem to 

 have become hardy under adverse circumstances and developing 

 under more favorable surroundings to a sturdier growth drive 

 out the feebler native plants. 



It does not necessarily follow because a plant was first described 

 from a given region, that it was there indigenous. It may well 

 be doubted, for iustauce, whether Agrimonia or Xanthium are 

 indigenous in North America; certainly, although widespread, 

 neither of them are so in California. 



Plants which are of annual or biennial duration, especially 

 those growing along the coasts, or in wet places, and belonging to 

 groups which find their chief development in distant regions, 

 should be rigorously scrutinized, and if possible compared 

 directly not only with the less-known species of the genus, 

 but also with those of the neighboring genera, in some one of 

 which it may have been already doubtfully placed. A recent 

 example of this is to be found in Howellia limosa} which appears 

 to have been at least once described before." Of course this does 



iD Greene, Pitt. ii. 81. 



i 2) '/ 'diviana Ph. M. 1 sjlaberrima; caule simplicissimo, debili; foliis ob- 



lonjjis, sessilibus, obtusis, apicem versus utrinque 2 — 3-denticulatis, omnibus ex axilla 

 Boriferis; floribus mi nulls, albis, petiolum xquantibus; laciniis calyciuis triaugularibus, 

 dimidiam corollam nee non filamentorutn column am sequantibus. 



ii ibitat in stagnulis pi teatit films Predericus. 



Caulis interdum pe tus, e parte inferiore radices Sliformes s<-u 



