WHAT IS A CACTUS? - THEIR DISTRIBUTION AND COUNTERFEITS----THEIR USES AND CLASSIFICATION.

IT IS always difficult to define a family of plants. Nature never consents to be buttoned up in a straight-jacket. Limits of groups are always flexible and indefinite, and nowhere more so, perhaps, than in the cacti. To most people a cactus is a curious plant - short and thick in stature, leafless and fleshy, deeply furrowed and beset with spines, but such features are not peculiar to these plants. There are many other plants to which they are common. To be sure, most of the cactuses possess these characteristics, but some of them are tall and slender, some have cylindrical and plain stems, some have true leaves, and many of them are spineless and smooth. Even the botanist finds difficulty in clearly defining them. He is obliged to disregard their forms and other general peculiarities, which are so apparent to common observers. The definitive characteristics of the family reside almost entirely in the flowers and fruit, and they may be stated in a rather loose way as follows :

The flowers are solitary and sessile; the sepals and petals are much alike, yet numerous and distinct from each other, and they imbricate or overlap in -several rows, and their bases are adherent to a one-celled ovary. The stamens are numerous, with long filaments, and they are inserted on the tube of the flower. The style is always single and the stigmas are many. The fruit is a more or less fleshy berry.

In shape the cactuses are perhaps the most various of all plants. Some are almost perfectly spherical, some are curiously flattened, some are angled, furrowed and grooved; many of them are column-like, and some are composed of curiously flattened joints, like an aggregation of a great many plates or thickened leaves one upon the other. The surfaces present the most surprising conformations, ranging all the way from perfectly plain rinds to those deeply furrowed, as in Echinocactus Visnaga (Fig. G), those composed of laminated or plate-like parts, as in the anhaloniums (Fig. N) or again to those presenting an exterior of curious polyhedrons, as in the six-sided echinocactus, E. hexicdrophorus (Fig. H).

In size they are equally various. Some are mere balls, which may be covered by the foot, while others rise in post-like trees to the height of 50 or 60 feet, with curiously elbowed branches like huge candelabra. Fig. A (page 451) represents a typical "cactus forest" of our southwestern deserts. Some of the low species attain great size. A specimen of Echinocactus Visnaga (Fig. G), which weighed a ton and measured over nine feet in circumference, was transported alive to England, in 1846, from Mexico.

For the most part cactuses are leafless, yet the pereskias (Fig. J) have true leaves; but in a certain sense the whole plant may be said to be one gigantic and curious leaf, for the green tissue of the entire surface acts in the capacity of foliage. The cactuses are inhabitants of exceedingly dry and hot regions, where evaporation from many leaves would be sure to destroy the plant. They have therefore through the evolution of ages taken on the form which presents the least possible surface to the air, and the moisture which fills their inner cavities is wonderfully protected from the dry atmosphere about them. They are also covered with a very hard epidermis, which serves the same purpose of preventing evaporation, and most of the species are clothed with numerous spines and hairs which also check the loss of moisture. These spines and hairs are nearly always characteristic of desert plants. Some have supposed that one of their chief functions is to protect the plant, for any animal which frequents desert regions would be very greedy of any plant which contains much moisture. Yet not all of cactuses have spines. There are some species even in arid regions which are perfectly smooth, but in such cases the epidermis is probably thick enough to sufficiently check evaporation.

Cactuses might be called vegetable jugs.

The armament of the cactuses is itself exceedingly various. It is oftenest made up of sharp and stiff spines. These vary in kind and number and manner of insertion. The number borne upon a tubercle is usually characteristic of the species. Two mam- illarias show these differences. M. micromeris (Fig. E), i. e., "small parts," has from 20 to 40 small spines upon each tubercle, while M. macromeris (Fig. A), "large parts," has only about half the number and they are very large and strong. M. macromeris is one of the largest flowered of all mamillarias. In fact, the flower is almost equal in size to the body of the plant. The covering of the old-man cactus (Cereus or Pihcereus senilis. Fig. CC) is mostly composed of long and white hair-like locks, while some species, particularly the opuntias, possess many small prickles which are detached by the touch and quickly enter the flesh. An old-man cactus was once estimated to bear 72,000 bristles, and upon a certain echino-cactus they were reckoned at 51,000.

The flowers of the cactus tribe are always singular and interesting, perhaps the more so because they are so entirely unlike in expression to the plants upon which they are borne. If the plants remind one of the most scorching deserts, the flowers, on the other hand, recall the choicest blossoms of the conservatory and the garden. They are exceedingly varied in form and color and size. The blossoms of the night-blooming cereus and the phyllocacti are among the most attractive and showy of flowers, while those of the rhipsalis are often inconspicuous. Yet this showy characteristic of the cereus flowers is by no means common to even the cereus tribe. The flowers of some of the species are small and almost green. Fig. Q, Cereus chloranthus, represents a species which has yellowish-green flowers, and their diminutive size can be understood when it is known that the entire plant rarely exceeds ten inches in height. This figure should be compared with Fig. A, which shows plants of the same genus, and with S, one of the night-blooming cereuses of the gardens.