CACTACEAE 
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menon is seen in Mammillaria, Cereus sp. &c. In some cases the 
growing point divides, during the growth of the mammilla, into two, 
one on the tip, the other in the axil, of the cushion. The latter gives 
rise to the fir. In Cereus, Echinocactus, &c. the stem is more or less 
cylindrical, bearing ribs on which are the areoles at regular intervals ; 
the rib is formed by the ‘fusion’ of mammillae, i.e. by the growth of 
the tissue under them during their development (cf. formation of sym- 
petalous corolla). In Phyllocactus, Epiphyllum, and sp. of Rhipsalis 
some or all of the shoots exhibit a flattened leafy form with areoles in 
notches on their edges. This form appears to be derived from the 
preceding by abortion of some of the ridges, and reversions are often 
seen (they appear if access of light be prevented). Lastly, other sp. 
of Rhipsalis show perfectly cylindrical stems. 
The bulk of the internal tissue consists of parenchyma in which 
water is stored ; the cell-sap is commonly mucilaginous, thus further 
obstructing evaporation. The cuticle is thick, and the ridges of the 
stem are usually occupied by mechanical tissue, whilst the stomata 
are in the furrows. Everything thus goes to check transpiration to 
the utmost extent; it is very difficult to dry a cactus for the herbarium, 
and its vitality is very great. Its growth is slow, but sp. of Cereus &c. 
reach a great size. Vegetative reproduction is frequent in the mam- 
millate forms, and occurs to some extent in others. In garden 
practice, cacti are often multiplied by cuttings, for a piece cut off 
and stuck into the soil will usually grow. Grafting is also largely 
resorted to. 
The firs, are usually solitary (exc. Pereskia), borne upon or near 
the areoles or in the axils of mammillae, large and brightly coloured, 
$ , regular or zygomorphic. Perianth (00), showing gradual transition 
from sepaloid to petaloid leaves, spirally arranged, often up the side 
of the ovary (cf. Nymphaea). Sta. 00, epipetalous. G (4 — 00 ), uniloc. 
with parietal placentae and 00 anatropous ovules; style simple. Fruit 
a berry, the flesh derived from the funicles. Endosperm or none. 
The fruit of many sp. is edible (e.g. Opuntia, &c.). Several sp. 
are commonly used in making hedges. The Cochineal insect is culti- 
vated on sp. of Nopalea, Opuntia, &c. 
Classification and chief genera (after K. Schumann) : 
I. CEREOIDEAE (succulents; leaves reduced to scales, often 
very minute ; no barbed thorns) : 
1. Echinocacteae (fir. funnel- or salver-shaped, in or near the 
areole) : Cereus, Phyllocactus, Epiphyllum, Echino- 
cactus, Melocactus, Leuchtenbergia. 
2. Mammillarieae (do., but in axil of mammilla): Mammil- 
laria, Pelecyphora. 
3. Rhipsalideae (flr. rotate) : Rhipsalis. 
II. OPUNTIOIDEAE (succulents with round or flat leaf-like 
joints; leaves cylindrical, usually falling very early; barbed 
