18 BULLETIN 31, U. S. DEPARTMENT OF AGRICULTURE. 



COLORATION. 



It is customary in descriptive works to place more or less de- 

 pendence upon the color of flowers, and authors usually have described 

 the color of the flowers they were dealing with quite faithfully. Un- 

 fortunately, little attention has been paid to the changes of color 

 which take place in the flowers from hour to hour during the day. 

 The descriptions therefore must be looked upon as depicting the 

 condition at one particular time only. Flowers of fully one-fourth 

 of the species change color decidedly as the day advances. On rare 

 occasions the flowers open the second day and then the change is 

 still more marked. Some change from light yellow to deep orange 

 with a tinge of red, some from light yellow to pink, others from brick 

 red to deep purple, etc. On the other hand, many species have vari- 

 ously colored flowers in different individuals, each changing or not, 

 as the case may be. One of the cane cacti of southern Arizona 1 has 

 flowers ranging from greenish yellow through chocolate to bright 

 purple, and two others 2 have almost as great a variation. 



The wealth and variety of green exhibited by these plants are 

 scarcely excelled in any other group, and the color of any one plant 

 is by no means constant. There is the color of the old, the young, 

 and the middle-aged joints, the autumn and spring color, as well as 

 the color of health, disease, and protection. The color of the young 

 growth is often strikingly beautiful, but similar colors may often 

 be produced by cold weather or at times by severe drought. Common 

 forms which exhibit this characteristic more especially are some of 

 the flat- jointed species. 3 



Species which are normally a bright or blue green color in their 

 native habitat upon the highland of Mexico are often more yellow at 

 the close of the hot, dry, cloudless summers of the Sacramento Val- 

 ley, while, unless injured by an exceptionally cold winter, they may be 

 even more deeply colored in the spring than they are in their native 

 heath. On the other hand 5 the members of the green glaucous group * 

 are, if anything, more gray than at home, while at Brownsville, under 

 seacoast conditions but still protected from the sea, the color is much 

 less striking. 



The conditions at Chico appear to make the gray, blue-green species 

 of the highland of Mexico more gray in autumn than they normally 

 woald be. This is probably due to the long, rainless summers. The 

 spring color of vegetative parts is, in nearly all species whose young 

 growth is tinted, brighter here than normal, although of the same 



1 Opuntia versicolor. 



2 Opuntia 8pino8ior and O. echinocarpa. 



"Opuntia phaeactmtha, O. chlorotica mntarita, and O. macmcentra. 



1 Opuntia rohusta. 



