96 



cross readily, giving rise to fertile hybrids. If the ranges of these 

 plants came to overlap there would arise a variable population 

 which no botanist arriving after the event could break up into two 

 species. 



Most remarkable is the recent production, — one may fairly say 

 creation, — of species through crossing. Miintzing crossed Galeopsis 

 pubescens with G. spcciosa, and was eventually able to extract a 

 plant which did not differ at all from the well-known species G. 

 tetrahit. This plant was fertile, and the stock can be carried on in- 

 definitely. Heribert Xilsson crossed the willows Salix caprea and 

 S. viminalis, and obtained a plant which morphologically could not 

 be distinguished from S. cinerea. Mrs. E. W. Erlanson, in a recent 

 paper on American roses, remarks: "Rosa rudiuscula is a natural 

 hybrid between R. Carolina and R. arkansana (the Western Prairie 

 rose), as I was able to prove by producing it experimentally. It is 

 so characteristic of the rose flora of northwestern Indiana, Illinois, 

 and eastern Iowa that it should be given specific rank." (Ameri- 

 can Rose Annual, 1932.) 



Species are not all of equal rank, if by that we mean antiquity 

 and distinctness, but on the face of the landscape they are real en- 

 tities, to be studied and discriminated. The recognition of sub- 

 species is a useful device for associating together minor types in 

 groups or aggregate species, and thus avoiding the excessive multi- 

 plication of independent binomials. It is quite true, as Dr. Gleason 

 indicates, that legitimate differences occur as to the placing of these 

 forms. In this sense it is perfectly true that the number of species is 

 a matter of opinion. But the number of different kinds of plants is 

 not, and it is I believe a dangerous and false doctrine (met with not 

 infrequently) that species do not truly exist in nature, but are 

 products of human mentality. I would put it this way. The pattern 

 of nature is woven in an intricate fashion, and it was so woven 

 ages before man came on the scene. It is man's opportunity to ob- 

 serve this pattern, recognize its details and reason about the oper- 

 ating causes. To do this is one of the highest functions of the 

 human mind. But truth must always be derived from reality, and 

 all departures from veracity are unscientific. 



The inevitable diagreements are partly due to mere mistakes, 

 to be corrected by further observation ; and partly due to differ- 

 ences of terminology, to be corrected by conference and agreement. 

 University of Colorado 

 Boulder, Colorado 



