94 



ranging from Guatemala northward to Alberta, Manitoba, 

 Ontario and Massachusetts; none are known to inhabit the 

 West Indies nor Central America south of Guatemala; those 

 here first described are Stipa saxicola from Puebla, S. leiantha 

 also from Puebla, S. constricta from Hidalgo, S. angustifolia 

 from Coahuila, and S. mexicana from Mexico and Hidalgo. 



Those inhabiting South America extend from Columbia and 

 Venezuela to Chile, Brazil and Argentina; Professor Hitchcock 

 recognizes eighty-nine species, describing nineteen of them as 

 new to Science. No species are known to exist in the Guianas 

 nor in northern Brazil. 



The geographic distribution of the genus and of its species, as 

 indicated by Professor Hitchcock, is significant. Its absence 

 from the hot tropical regions, both insular and continental, 

 implies physiological adaptation to the lower temperatures; 

 from the Guatemala locality of Stipa Ichu (Volcano Agua), to 

 the mountains of northern Colombia, where several species 

 occur, is a distance of about lo degrees of latitude or about 

 700 miles, through which no species are known to exist, and 

 probably do not exist unless as rarities as yet unobserved. 

 From central Florida {Stipa avenacioides) to northern Brazil, there 

 is a much greater gap of about 2i degrees, or about 2400 miles. 



Considering individual species, this striking discontinuous 

 distribution appears as follows: — 



Stipa speciosa, Colorado to California and Lower California — 

 Bolivia, Chile, Argentina. 



Stipa Ichu^ San Luis Potosi to Guatemala — Colombia to 

 Bolivia and Argentina. 



Stipa tenuissimay Texas and New Mexico to Puebla — Argen- 

 tina. 



Stipa mexicana, Mexico and Hidalgo — Colombia, Venezuela, 

 Peru. 



Stipa mucronata, Nuevo Leon to Tlaxcala — Colombia to 

 Chile and Argentina. 



While similar discontinuous distribution is well known in 

 other plants, these detailed studies of Stipa provide a convenient 

 opportunity for calling attention to it as a very interesting 

 phenomenon, its cause or causes as yet obscure, perhaps attrib- 

 utable to migratory birds. 



The three plates of figures contain illustrations of the fruits 



