metimes about 6 in. high, those
surrounding it being shorter and shorter, till the outside ones rise
only just above the soil. A well-grown plant of this is strikingly
pretty, even when not in fruit. It is a native of Mexico, and requires
the treatment of a warm house. A few pieces of broken brick should be
placed upon the surface of the soil about the base of the plant, as the
stems like to press against, or grow upon, anything in the nature of
rocky ground.

M. echinus (hedgehog-like); Fig. 59.--A distinct and pretty little
plant, the largest specimen having a stem about the size and shape of a
small hen's-egg, completely hidden under the densely interwoven radial
spines, which crown the thirteen spiral rows of tubercles, and are
almost white when mature. The tubercles are 1/2 in. long, and, in addition
to these white radiating spines, they also bear each a stout spike-like
spine, growing from the centre of the others. This spine gives the plant
an appearance quite distinct from all other cultivated Mamillarias. The
flowers are produced two or three together, on the top of the stem, and
they are nearly 2 in. long, cup-shaped, and coloured yellow; they usually
appear about June. As yet this species is rare in cultivated
collections. It comes from Mexico, where it is found growing on
limestone hills, in hot and arid localities. Under cultivation it
requires a warm greenhouse temperature, exposure to bright sunshine all
the year round, with a moderate supply of water in summer, and none at
all during winter. A few large pieces of broken brick or sandstone
placed in the soil, just under the base of the stem, afford the roots
conditions suitable to their healthy growth.

[Illustration: FIG. 59. MAMILLARIA ECHINUS.]

M. elegans (elegant).--A small species, grown only for the prettiness
of its stem, flowers rarely, if ever, being borne by it under
cultivation. The stem is 2 in. high and wide, globose, with small conical
tubercles, which, when young, are woolly at the tips. Spines short and
slender, about twenty, arranged in a star on each tubercle, with four
central ones a little longer than those which surround them; the colour
of the spines is whitish, with brown tips. Native country Mexico, on
high exposed hills; in this country it requires greenhouse treatment.
Introduced about 1850.

M. elephantidens (elephant's-tooth); Fig. 60.--One of the largest and
most remarkable of all garden Mamillarias. Stem globose, depress