CACTI 15 



The species of the group are very floriferous, the prevailing color 

 being a deep rose purple, but there are white-flowered forms in most 

 of the species and varieties. The plants are all low but erect, spread- 

 ing, and mostly one to three joints high except Opuntia huTrdstrata, 

 which is prostrate. The whole group varies greatly in coloration 

 of plant body, as do many species of cacti. Some are bright to 

 glaucous green, others bear a reddish cast, while the young growth 

 k as well as the old in cold weather are copperized, giving very pleasing 

 I effects. These facts, coupled with their wonderful symmetry and 

 compact growth, make the group very advantageous for some settings, 

 and they are greatly admired and sought after. 



The chief attractiveness and beauty in cacti as a group is the 

 remarkable symmetry of growth in the individual plants. This is 

 particularly well brought out in Plates 3, 9, and 11. The columnar, 

 and most of the genera of smaller cylindrical or globular forms, 

 have clean-cut, longitudinal, parallel angles, ribs, or wings, and 

 located on them at regular, intervals are the buds, or pulvini, which 

 bear the spines and flowers and from which side branches may be 

 developed. The coloring of the epidermis of the plant is frequently 

 very attractive. .While in most species this color is some shade of 

 green, many specimens are coated over to a greater or lesser extent 

 with white or bluish bloom. In some species the surface is dotted 

 with very small bunches of velvety white hair, as in Astrophytum 

 {Echino cactus) rrvyriostigmm (pi. 11, B), A. (E.) omatum, and A. 

 (E.) capricornis. Other species are mottled with purple, which 

 in the young growths of Echinocactus ingens is arranged in trans- 

 verse bands alternating with bright green. The coloring of the 

 spines, too, is often exceedingly attractive, especially in the younger 

 growths. It ranges from pure white to amber, yellow, red, and black. 

 Frequently some of these colors are combined on one spine in either 

 longitudinal stripes or transverse bands, and the perfectly uniform 

 variegation is very striking. The form, structure, and arrangement 

 of the spines are in most instances remarkable and show a wonderful 

 adherence to a definite plan of symmetrical arrangement. In certain 

 species some of the spines have a structure of soft and hard trans- 

 verse layers from base to tip, giving an uneven though uniformly 

 wavy surface much like that of a goat's horn. The larger number of 

 spines are straight or only slightly curved; others have the end 

 curved in the form of a fishhook. Nearly all of them are rather 

 stiff, but some are soft and featherlike in structure and others are 

 thin, flat, paperlike, and flexible. Again, in some species the spines 

 are entirely absent. 



Mammillaria (pi. 3, A, B, C, and D) and some groups of Echino- 

 cactus have all the variations of characters already described, but 

 they differ materially in body structure. In them the ribs or angles 

 have entirely disappeared and are represented by rows of tubercles 

 I or mammae, each bearing at its summit a cluster of spines. In this 

 group the tubercles are not arranged in longitudinal rows, but are 

 geometrically tessellated over the plant surface, so arranged as to 

 form spirals running in both directions about the plant. 



A remarkable and interesting feature is the regularity in number 

 with which these spiral rows appear. As a rule, they fall into the 

 numbers 5, 8, 13, 21, 34, 55, and possibly higher numbers. For 



