THE FLORAL WORLD AND GARDEN GUIDE. 229 



Cereus, though I know of no cause why they may not be, as the 

 differences in the flowers are not differences of structure, but merely 

 degrees of development ; such as a greater or lesser number of 

 stamens aud petals, or in the absence in some, and length in others, 

 of the tubes of the corolla, excepting that it may be that the pollen 

 tubes might be too strong for the distance they have to grow from 

 the apex of the stigma, or vice versa. 



The chief points to be observed in the foregoing directions are, 

 the light, time, and mode of potting, taking special care not to be 

 afraid to cut off the roots. The watering — which should be given 

 with a rose on the pot — when given, let it be enough to thoroughly 

 soak the soil. It is best to hold the pot as high as you can, so that 

 the water may fall on all parts of the plant, which serves the double 

 purpose of washing and watering at the same time. Be sure to give 

 them a good drying in the winter, upon which depends the success 

 in flowering them the next season. 



Some few species, as Opuntia vulgaris, and Rafinesquicma, and 

 Eclrinopsis Eyriesii, are hardy in the south of England ; and I have 

 no doubt that many species of Opuntia and Echinopsis would do 

 very well in cold frames in winter, and the open air in summer. Eor 

 an amateur, the Cacti are the best class of plants to cultivate, as they 

 offer the greatest scope for number of species, and require so little 

 attention. In a house 20 feet by 12, from 400 to 500 species 

 may be grown ; in the summer the house can be left night and day 

 with air ; and if the owner had no person he could trust, he might 

 lock the house and leave them a week at a time without fear of 

 harm. In the winter, if he should be obliged to leave home, the 

 only thing would be to get the heat looked after, and his pets would 

 welcome him home with as fresh an appearance as when he left. 



SEMPERVIVUM ARBOREUM. 



JHIS Sempervivum, which is perhaps better known as the 

 " Tree Honseleek," is one of the finest of the succulents 

 of free growth for the greenhouse of the amateur culti- 

 vator, and for the window. It is readily multiplied, 

 and it is so remarkably free in growth, that the pro- 

 duction of a specimen with a fully-developed head is, comparatively 

 Bpeaking, a very easy task. The side-shoots taken off an inch or so 

 from the main stem, and inserted in small pots filled with light sandy 

 Boil, will, if placed in a sunny position in the greenhouse, soon strike 

 and become established. To encourage a vigorous growth, repotting 

 annually, or every second year, will be necessary ; but as _ over- 

 potting is most injurious, pots one size larger than those previously 

 occupied must be employed at each shift. A thorough drainage is 

 essential, and a compost consisting of turfy loam, small crocks, and 

 sand is the most suitable. There is a fine variety, witli deep bronzy- 

 purple leaves, and one with variegated leaves, and these are known 



August. 



