114 CACTUS CULTURE FOR AMATEURS- 



0. Rafinesqu.ii. Thrives in a sunny position out of doors where 

 it can be protected from frost and excessive wet. It flowers in 

 early summer. (Fig. 59.) 



O. microdasys. 



Stem short, with flattened joints, which are nearly circular in 

 outline, and are covered with little cushions of bright orange-yellow 

 bristles. Mexico. Thrives in a warm greenhouse. Grows best 

 when grafted on a robust- growing kind. There is a variety named 

 rufida, in which the bristles are reddish-brown. 



O. polyacantlia. 



Stems prostrate, forming large, spreading masses under favour- 

 able conditions. Joints broad, flattened, obovate, about 4 inches 

 long by 2 inches wide, light green ; spine- cushions less than 1 inch 

 apart, and composed of numerous small, white spines, with from 

 one to four longer ones ; these latter fall away when the joints get 

 old. Leaves very short, with a little wool about their bases. 

 Flowers 3 inches in diameter, appearing from May onwards ; petals 

 yellow, dashed with rose, sometimes wholly rose-coloured or brick- 

 red. Stamens deep red ; pistil yellow, with a conical stigma. Fruit 

 nearly round, spiny, about 2 inches long. Wisconsin and the San 

 Francisco Mountains ; introduced in 1814. This is as hardy as 

 0. Rafinesguii, and thrives under similar treatment. It has stood 

 22 deg. of frost in this country. In North America, where it forms 

 large, spreading masses on gravelly hillsides, it is usually covered 

 with snow from Christmas to May. There are several varieties of it. 



O. monacantha. 



Stems robust, not unlike 0. Dillenii in general habit. Joints 

 flat, large, oblong or ovate in outline, rather thinly compressed, 

 and bearing grey cushions over 1 inch apart, with a solitary spine, 

 1 1 inches long, spring from the centre of each cushion, and pointing 

 downwards. Flowers sulphur-yellow, 2- inches across, borne on 

 the young joints in May. Fruits ovate, 2 inches long, green, with 

 tufts of short, brown bristles ; pulp edible. Brazil, but now common 

 in many tropical and sub-tropical countries. It forms a large 

 specimen if planted in a bed of brick- rubble, in a warm greenhouse. 



O. nigricaiis. 



Stem stout, erect, hard and woody when old. Joints flat, 

 oval 5 to 8 inches long. Cushions 1^ inches apart, composed of 

 short reddish- brown bristles and two or three long stout spines, 

 which are yellow when young, but almost black when ripe. Flowers 

 produced in August on the young, ripened joints, orange-red, about 

 3 inches across. Fruit pear-shaped, crimson when ripe. Brazil. 

 Thrives in a warm greenhouse. At Kew a large specimen 12 feet 

 high, with an enormous head, had to be cut down because of its 

 top-heaviness. Its head was planted as a cutting. 



