November 8, 1901.] 



SCIENCE. 



723 



as does the still lighter green of the tall 

 knot weed (^Polygonum ramosissimum) , while 

 the nearly similar pale green of the buffalo 

 grass {Bulbilis dactyloides) turns to a silvery 

 gray. On the other hand, the richer green 

 of the switch grass (Panicum virgatum) 

 turns to a red orange below and a light 

 yellow above, and the dark green of stink- 

 weed (Dysodia papposa) as seen in the sum- 

 mer is replaced in early winter by a pro- 

 nounced brick-red. Yet in the midst of 

 these changes the clumps of dagger weed 

 ( Yucca glauca) and the bunches of cactus 

 ( Opuntia humifusa and 0. polyacantha) retain 

 their green color, and in fact, are the only 

 green things in the landscape. 



I may summarize the facts so far as I 

 have observed them by grouping the plants 

 under the colors they assume, as follows : 



RED. 



Bunch grasses (Andropogon furcatus, and 

 A. scoparius). 



The first (tall bunch grass) is some- 

 times of a rich orange-red running to dull 

 red, and the second (low bunch grass) is 

 from brownish red to brick-red and purple, 

 fading out sometimes to a dull gray. 



Knotweeds {Polygonum ramosissimum and 

 P. emersum), with the stems of various 

 shades of red, in the second species running 

 to purple red. 



Willows (Salix fluviatilis) with red twigs. 



Stink weed (Dysodia papposa), \yhole plant 

 becoming brick- red. 



ORANGE. 



Bunch grass (Andropogon furcatus); as 

 noted above, this species sometimes assumes 

 a rich orange-red color. 



Switch grass {Panicum virgatum) the 

 lower portions of the seeding plants are 

 often of a red-orange color. 



YELLOW. 



Maize fields during the autumn and early 

 winter assume many shades, from the 

 deepest yellow to a pale straw color. 



Switch grass (Panicum virgatum); the 

 upper portions of the seeding plants are 

 often of a light yellow color. 



GREEN. 



Dagger weed ( Yucca glauca) and prickly 

 pear cactus ( Opuntia hemifusa and polya- 

 cantha) constitute the only green vegetation 

 on the plains in the winter. 



BLUE. 



Plum thickets (Prunus americana), seen 

 at a little distance are distinctly of a dark 

 blue color. 



PURPLE. 



Sumach fruits (Rhus glabra) , ranging from 

 a dull purple to a rich maroon-purple. 



Low bunch grass (Andropogon scoparius), 

 as noted above this species ranges from dull 

 red to purple. 



Knotweed (Polygorium emersum) although 

 usually red, sometimes it becomes a purple- 

 red. 



BROWN. 



Eussian thistle (iSalsola tragus), brown to 

 blackish-brown, and the same may be said 

 for weed fields in general. 



Plum twigs (Prunus americana); although 

 plum thickets when seen at a little distance 

 are dark blue, the twigs when seen near at 

 hand are reddish brown. 



Box elder fruits (Acer negundo), light 

 brown, and as they are very abundant they 

 give the trees their color when seen near by. 



BLACK. 



Cottonwood tree trunks and branches 

 (Populus deltoidea) seen at some distance 

 are brownish-black to black. 



Plowed land, burned areas and wagon 

 trails all show black or nearly so on the 

 landscape. 



GRAY. 



Buffalo grass (Biibilis dactyloides), from a 

 light or silvery green in the summer, this 

 species changes to a light gray or silvery 

 gray in the winter. 



