V. GRANT 61 



give rise to serious difficulties of species delimitation. Further- 

 more, so far as the botanist can judge from the study of numerous 

 cases of natural hybridization, the process of secondary specia- 

 tion does not necessarily always go to completion, but may re- 

 main more or less indefinitely in an undefined halfway stage. 



Asexual Reproduction. The reversion to asexual reproduc- 

 tion, as numerous authors have pointed out, spells the end of 

 species in the biological sense of the word. The smallest inte- 

 grated unit above the individual is the clone or biotype; the 

 smallest well-defined taxonomic unit may be a huge polymorphic 

 complex, an agamic or clonal complex. 



For purposes of classification the taxonomist must name and 

 describe selected morphological types in asexual groups. Whether 

 these aggregations of individuals should be called "species" or 

 not is a matter of taste. One tradition favors a general and hence 

 indiscriminate use of the category of species in all groups of or- 

 ganisms. Some botanists would qualify this usage in asexual 

 groups by employing the terms agamospecies or taxonomic spe- 

 cies. The term agameon has also been suggested (Camp and 

 Gilly, 1943). 



The present author prefers the neutral term, binom, suggested 

 by Camp ( 1951 ) . The grounds for this preference are that it 

 saves the term species for the isolated population system and 

 avoids the confusion of concepts inherent in the application of 

 the same word to two basically dissimilar phenomena. 



In summary, the existence of the species as an objective bio- 

 logical unit is not impaired by morphological indistinctness or 

 by the continuity of the evolutionary process. The loss of sex- 

 uality, on the other hand, removes the very foundations on which 

 the species exists as a type of breeding population. As a result, 

 biological species do not exist in asexual groups. 



The consequences of natural hybridization for the biological 

 species concept cannot be stated so categorically. The discrete- 

 ness of the species unit is a relative matter in a hybridizing com- 

 plex. An attempt to evaluate the significance of natural hybridiza- 

 tion for the objective reality of species will be made in the next 

 section. 



