J 



62 



nizing as species those entities with well-marked characters 

 that maintain these characters over a considerable part of their 

 range, even though they intergrade completely with some other 

 species in certain regions, particularly where this intergradation 

 is between forms that are obviously not closely related." These 

 observations are bound to have an important place in all future 

 treatments of natural hybrids. 



The Villosae and Micranthae are the most primitive forms 

 of the genus and both groups have species in the southern 

 Appalachians. Although they represent primitive Tertiary 

 stock, time has not been sufficient for them to spread into Asia. 

 The Hemsleyanae of western United States appear to have come 

 from certain Micranthae, isolated in the mountains of Mexico 

 at an early period. 



With the Western species and their subdivisions in the main 

 taxonomic treatment (pp. 26-174), the reviewer has not had 

 sufficient contact to pass judgment, but reduction of H. macro- 

 rhiza of the Alleghenies to a variety of H. villosa receives his 

 whole-hearted approval. 



This paper has been prepared with care, as may be seen 

 from the geographic notes on obscure places and the cited de- 

 tails of Nuttall's itinerary in "Oregon" (p. 163, 164). Even the 

 little slip-ups, which inevitably occur in a work of this scope, 

 for example "Hort. Bldg." for "Hort. Belg." (p. 175, 176), are 

 very infrequent; one obvious error, the lack of a specific name 

 for Heuchera alpestris (p. 104) has been subsequently supplied 

 by the authors themselves. The publication under review is not 

 only the last word on Heuchera for systematic botanists, but it 

 should be in the hands of all geneticists who are interested in 

 the actual occurrence of hybrids in nature, and of horticulturists 

 who contemplate growing these attractive plants. 



H. K. SVENSON 



