GRIFFITHS THE GRAMA GRASSES. 



377 



on the ventral surface, the scutellum covering over three-fourths of the ventral surface. 

 (Plate 72, A, B. Figure 35.) 



This is without doubt the most important economic species of the genus, extending 

 from Manitoba to South America. It is doubtfully reported from Tampa, Florida. 

 As would be expected from a plant of such wide range, it is extremely variable. The 

 above description is drawn in the main from my no. 6108 from the Sonoyta Valley of 

 Arizona, which is very different from the plains region form. The latter produces a 

 rough, rather bunchy sod and sends up but few culms, the abundant basal leaves 

 forming a curly covering close to the ground, the species on this account often being 

 confused in the popular mind with the buffalo grass (Bulbilis dactyloides) . But in the 

 southern desert region where, along the Mexican border, it grows in abundance at an 

 altitude of about 5,000 feet it is usually in isolated large bunches. In favorable 

 situations in swales such as are found on the eastern slope of the Santa Rita Mountains 

 of Arizona it assumes more nearly the appearance of the northern form so far as habit 

 is concerned (PI. 72, B). In the South the plants usually grow much larger. It is 



Fig. 35. — Bouteloua gracilis, a, Spikelet; 6, c, lemma and palet of first floret; d, e, rudiments of second 

 and third florets, a, Scale 7.5; b-e, scale 15. From type specimen of B. stricta. 



not at all uncommon to find plants there 60 or 70 cm. high, while upon the prairies 

 of the Dakotas the species seldom grows over half as high. 



The difference in habit has been assumed by some to indicate a different species, 

 but after studying the species from North Dakota to Oaxaca and cultivating it several 

 times I am not able to take this view. It must be considered that the prairie form of 

 the Dakotas and Montana occurs not only upon the cold, high prairies of the north, 

 but upon the high tableland of northeastern New Mexico (PI. 72, A), upon the San 

 Francisco highland of northern Arizona, upon the Santa Rita highland of southern 

 Arizona, and in many isolated localities in highland Mexico. This low turf -forming 

 form passes by imperceptible gradations into the tall, robust, strictly bunchy form 

 represented best by the type of B. stricta. 



Explanation of Plate 72.— A. A growth of Bouteloua gracilis under plains conditions in northeastern 

 New Mexico. For several years this locality has been grazed during the winter months only. B. A 

 turf of Bouteloua gracilis at an altitude of 5,000 to 6,000 feet. Compare with figure A. This species does 

 not form a turf thus far south, except at a considerable altitude and under favorable soil and moisture 

 conditions. 



