346 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



The spikes of many of the species also drop off very readily when 

 they approach maturity, and it is thus difficult to save the seed. 

 So pronounced is this tendency in some species that it is impossible 

 to prepare good herbarium specimens of plants in the mature state. 

 This accounts for some of the taxonomic errors that have crept 

 into our conceptions of the species. Collectors have commonly 

 selected plants which could be made into good herbarium specimens, 

 or, having collected mature ones, the spikes have been lost. 



Bouteloua gracilis (PL 69, B) makes a splendid turf when sown 

 thickly and well cared for. In some places upon the native prairies 

 and foothills of the Northwest beautiful natural turfs of this and 

 Bulbilis are common. Although the quality of the turf is good it has 

 the disadvantage of being green but for a short season. 



In short, it is more than probable that, because of the lack of good 

 seed habits in this genus, even the most valuable species can not 

 become of importance in cultivation, although good yields of hay 

 can be secured from B. curtipendula at least (PI. 69, A), and good 

 stands can be secured with any of the other perennial valuable species 

 if the seed be secured and sown thick enough. 



DISTRIBUTION. 



It is exceedingly difficult to give any definite and concise informa- 

 tion regarding the altitudinal distribution of the species. Bouteloua 

 gracilis is at home upon the prairies at an altitude of 1,000 feet, and, 

 as we have seen, the same form occurs at 7,000 feet or more in the 

 San Francisco highland of Arizona, and at much lower levels in the 

 Santa Rita Mountains, while the taller form grows as low as 4,000 

 feet in the Santa Rita Mountains of Arizona. Precipitation is a 

 much more important factor than altitude. So far as temperatures 

 are concerned, B. gracilis endures —40° F. in the northern plains 

 and makes a good growth in nearly frostless regions upon the high- 

 lands of central Mexico, while it sometimes endures a maximum of 

 100° F. in the summer season. 



In a circumscribed Bouteloua area there is quite a well-marked 

 zonal distribution of some of the species (Pis. 68, B; 70, A, B; 

 71, A, B). As an example may be mentioned the region north of 



Explanation OF Plate 70. — A. Scene from north of the Santa Rita Mountains in southern Arizona. 

 In the foreground B. aristidoides predominates and B. parryi is common. A little farther out B. rothrockii 

 and B. filiformis are the prevailing species. On the lower portion of the steep slopes B. curtipendula and 

 B. hirsute, are very abundant, the former reaching an altitude of 5,000 feet, about the highest points at the 

 left of the picture. About one-third way up the sides of the mountains to the right B. radicosa is abundant, 

 while on southern exposures at the altitude of the small cone in center of picture B. eludens occurs sparingly. 

 B. A portion of the same area close to the mountains to the right, as seen in the spring of the year. Compare 

 these with plate 75, B. It will be seen that the crop of grass, mainly Bouteloua, is all eaten off and there 

 is now a crop of annual weedy plants consisting mainly of Plantago, Pectocarya, Eschscholtzia and a few 

 small annual composites. 



Explanation of Plate 71.— A. A closer view of ground shown in the left-hand part of plate 70, A, 

 showing summer condition of region similar to that shown in plate 70, B. The gramas in the foreground 

 are mainly B. curtipendula, B. hirsuta, B. filiformis, and B. eriopoda. Dasylirhn wheeleri also shows 

 prominently. B. Scene in the Altar Valley, Arizona, Baboquivari Peak in the background. In the 

 foreground are shown B. rothrockii, B. barbuta, B. aristidoides, and B. filiformis. 



