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. 
Boutelowa 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 (Pl. 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 (Pls. 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, 
Tn the foreground B. aristidoides predominates and B. parryi iscommon. A little farther out B. rothrockit 
and B., filiformis are the prevailing species. On the lower portion of the steep slopes B. curtipendula and 
B. hirsuta 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. Dasylirion wheeleri also shows 
prominently. B. Scene in the Altar Valley, Arizona, Baboquivari Peak in the background. In the 
foreground are shown B. rothrockii, B. barbata, B. aristidoides, and B. filiformis. 
