DISTRIBUTION OF THE MOEE PROMINENT NATURAL ORDERS. 279 



genera, represented by 454 species ; and the numbers for North Mexico are fifty-seven and 

 184 respectively. The most considerable American extension of these genera and species 

 is into South America, where no fewer than eighty-five of the genera are represented by 

 the same or other species ; and 185 of the Mexican and Central- American species actually 

 extend into South America. In point of numbers the West Indies come next. The 

 northward extensions are much lower than might have been expected for this order of 

 plants ; this is specially emphasized in the species. Fifty of the Mexican genera are 

 found in western North America, as defined for the purposes of this work, and sixty- 

 two of the species enter the same region, though very many of them do not range beyond 

 Texas, New Mexico, and Arizona. But, what is more surprising, only quite a small 

 number of grasses are common to California and Mexico, It is true that the Monocoty- 

 ledonous orders generally have more species common to Mexico and eastern North 

 America than to Mexico and western ; yet it is not so markedly exhibited by any other 

 large order as by the grasses. Fournier, indeed, could enumerate only three grasses 

 common to California and Mexico, namely, Panicum fimbriatum, Tripsacum dactyloides, 

 and Sporobolus virginicus * ; but we are able to add to the list f. We find the following 

 species common to the two countries : — Cenchrus tribuloides, Phalaris arundinacea, 

 St/ipa eminens, S. viridula, Sporobolus cryptandrus, Epicampes rigens, Agrostis scabra, 

 A. varians, A. verticillata, Bouteloua aristoides, B. oligostachya, B. polystachys, 

 Monanthochloe littoralis, Bromus ciliatus, Ilordeum jubatum, and Elymus sitanion. 



Forty-eight genera and sixty-four species are common to Mexico and eastern North 

 America; but figures alone do not adequately express the degree of extension. It will 

 be perceived that the numbers are nearly the same as the western ; but a much larger 

 proportion of the species are common and widely spread, and, one might say, charac- 

 teristic of the whole eastern side of the northern continent. Fournier directs attention 

 to this fact in the work cited. According to his material, thirty-three of the Mexican 

 grasses were common to Texas, and sixty-five to the Eastern States. 



It is also noteworthy that the only member of the Andropogoneae hitherto found in 

 California is Ischcenum leersioides, Munro, a native of Southern China, colonized near 

 San Francisco ; yet they are not uncommon in the Atlantic States. 



The endemic genera are Euchlcena, Schaffnera, Bauchea^ Jouvea, Opizia, and Cala- 

 mochloa. Euchlcena is a remarkable and interesting grass, most nearly allied to the 

 maize (Zea), having the sexes similarly separated, and very long exserted styles* 

 Several of the endemic grasses of the Texano-Mexican region are remarkable for the 

 complete separation of the sexes, either monceciously or diceciously %. To this category 

 belong Jouvea, Opizia, Buchloe, and Scleropogon (see Plate 101), the last-named 

 inhabiting Mexico and New Mexico and recurring in Mendoza. 



* Mexicanarum Plantarum Enumeratio, Glumacese, Introd. p. xv. 

 t Watson's Botany of California. 



X Fournier, "Sur les Graminees mexicaines a sexes separes," Bull. Soe. Bot. Belg. xv. 1876 y pp. 459- 

 476. 



