16 CIRCULAR 6 6, U. S. DEPARTMENT OF AGRICULTURE 



example, if it is found that there are 13 parallel rows of tubercles 

 running obliquely around the plant in one direction, there will be 

 either 8 or 21 such parallel rows running obliquely around it in the 

 other direction. Whatever the number of rows counted in one direc- 

 tion, the number counted in the opposite direction will be the one 

 either preceding or following it in the series. Exceptions to this rule 

 are rare, and when one is noted the numbers are usually found to be 

 the doubles of two adjacent numbers in the above series, as 10, 16,/ 

 26, 42, and so on. Another interesting fact is that each number nr 

 the series is the sum of the two immediately preceding it. 



While symmetry is the greatest attraction in this group of plants, 

 monstrosities are not infrequent in the family, usually assuming a 

 cristate or cockscomb form of growth. (PI. 14, A; and pi. 11. C.) 

 These forms are so odd in appearance that they are always sought 

 after, and it is common to find them represented in the collections 

 of amateurs. Their very grotesqueness commends them to the con- 

 sideration" of collectors. They are found in all groups, but occur 

 most frequently in the columnar species of many genera, particularly 

 in Cereus and Opuntia and their allies. The forms are usually 

 designated by the term "cristata" following the scientific name of 

 the plant. They command a high price, usually twice as much as 

 the normal forms or more. A rare and beautiful example of this 

 kind of variation is shown in Plate 14, A. 



SINGLE-PLANT DISPLAYS 



Each individual plant has an attractiveness of its own (see pis. 3, 

 A ; 9, B ; and 10) , whether it be the symmetrical order of its trunk, its 

 color, its versicolored or versiform spines, or a combination of all 

 these features, supplemented in its proper seasons by the production 

 of flowers and fruits. Each normal, healthy plant is well worthy 

 of consideration as an individual specimen. The adaptability of 

 individuals is such as to commend them for situations where many 

 other plants could not exist. They do not require frequent repotting 

 and replenishing of soil, and subsist best on a periodical distribution 

 of water, so that if necessarily neglected for a time they do not ma- 

 terially suffer. A single plant is well worth the little trouble re- 

 quired for its keeping. It occupies a very small amount of space in 

 comparison to its weight, which is an advantage in many instances. 



A pretty and interesting display may be had by arranging the 

 plants in groups on benches, on window sills, or on bracket shelves 

 on either side of a window. Pots of individual plants of various 

 sizes lend themselves very readily to artistic arrangement. In any 

 banking effect the larger and taller ones should be placed in the 

 background and the rest graded down to the front according to the 

 size of the plants. Should the plants be too uniform in size for such 

 an arrangement, those in the background may be elevated on in- 

 verted pots or blocks of wood of suitable height. 



GROUPINGS 



Pleasing effects may be obtained by placing a number of plants 

 in one pot or small box. For this purpose it is necessary to choose 

 small plants, preferably the low-growing globular or snort, cylin- 

 drical forms of Mammillaria and Echinocactus. With a little care 



