24 



of Professor Wolf. There was a whole group of plants, indeed, wliich 

 we found nowhere else. Amono- them were Prinudn. Pnrrui 



ijf 



Saxifraga 



In September this camp was broken up and the party moved to the 

 San Luis Valley, via the valley of the Upper Arkansas and Poncho 

 Pass. Thougli late in the season, a fair number of plants not hitherto 

 found by us were collected. 



We remained several weeks in the valley, adding largely to the col- 

 lectioii, and toward the last of September started for Loma, on the head- 

 waters of the Eio Grande. Owing to the lateness of the season, but 

 few plants were obtained here. Among them were some novelties to 

 the collection. I would especially name Loma as a point worthy of fur- 

 ther botanical work. At this place plant-collecting was abandoned for 

 the season. 



FLOE A OF THE OPEN GROUND. 



T4ie most obvious division of the botanical regions traversed during 



the past season would be into the oi^en grounds, including under this 



head the plains from Denver to the foot-hills, the flat portion of South 



Park, the iuimediate valley of the Arkansas, and San Luis Valley 



proper. There would then remain the mouutaiu-region, incliuUng here 



the entire flora from the lower limit of timber to the highest mountain- 

 tops. 



There is at first sight a wonderful sameness about the flora of the 

 plains, which has not escaped the notice of casual observers. The 

 hoary, dry, stunted plants, with the great preponderance of yellow and 

 red flowers, when compared with the more living aspect of the mount- 

 ain-flora, actually compels a contrast in the mind. 



To what is this diflerence due ! Meteorological statistics from Colo- 

 rado are as yet meager in the extreme. Up to 1872 from only three 

 points did we have observations for a period of over one year. Such 

 at least is the showing of Mr. Schott's " Tables and results of the pre- 

 cipitation in rain and snow in the United States," and neither of these 

 points was fairly within the grasp of the mountains, so that any com- 

 parison must be somewhat lame. If, however, we sum up, and average 

 the fall of rain and snow at Forts Garland, Massachusetts, and Lyon,'it 

 appears that the mean amount is 12.09 inches. This, however, can only 

 be taken as an approximate estimate for the more open country just 

 east of the main divide, beiug probably greater than the fall farther 

 east, and certainly less than that west. 



series of years in West 



for a 

 t has 



some points of similarity to Central Colorado, and because its precipi- 

 tatiou IS tar trom excessive. The difference is so great as to su^'-ffest 



that this is an essential feature in thediffereuceof the floras in Colorado, 

 where we probably have a difference as great between the meteorolo"-i- 

 cal conditions of its plains and its mountains. 



Another meteorological element will probably be sufficicut to explaiu 

 the problem m part. Where we have so small a mean precipitation, it 

 IS sate to inter that the atmosphere comparatively seldom reaches the 

 point of saturation; L e., that there is less than the ordinary amoluit of 

 aqueous vapor in it. Then it follows that however much of the sun's 

 heal be absorbed by the soil during the day, it will be most freely radi- 

 ated back into space at night. I cannot better illustrate the full import 

 ot this tact than by a quotation at second hand from Tvndull : "Aqueous 



