ON CACTI AND OTHER SUCCULENTS. 789 



with Fir-tree oil or tobacco-water will answer. Hot water may 

 also be successfully employed, turning the pots on their sides 

 when using the syringe. Water as hot as the hand can bear 

 will not injure the plants. 



Having now given a brief outline of the treatment ot 

 succulents, we will proceed to consider the chief genera and 

 species as far as space will permit. 



In the identification of plants of the various genera, the following 

 " keys," given by W. Watson in his " Cactus Culture for Amateurs," 

 will be found most helpful : 



Tribe I. — Calyx-lube produced beyond the Ovary. Stem covered with 

 Tubercles, or Ribs, bearing Spines. 



1. Melocactus. Stem globose; flowers in a dense cap-like head, com- 

 posed of layers of bristly wool and slender spines, amongst which the small 

 flowers are developed. The cap is persistent, and increases annually with the 

 stem. 



2. Mammillaria (including Ajthalonium). Stems short, usually globose, 

 and covered with tubercles, or mamma;, rarely ridged, the apex bearing spiny 

 cushions ; flowers mostly in rings round the stem. 



3. Pelecyphora. Stem small, club-shaped ; tubercles in spiral rows, 

 and flattened on the top, where are two rows of short scale-like spines. 



4. Leuchtenbergia. Stem naked at the base ; tubercles oa the upper 

 part large, fleshy, elongated, three-angled, bearing at the apex a tuft of 

 long, thin, bristle-like spines. 



5. ECHINOCACTUS. Stem short, ridged, spiny ; calyx-tube of the flower 

 large, bell-shaped; ovary and fruit scaly. 



6. Disocactus. Stem short ; calyx-tube thin, the throat filled by the 

 stamens ; ovary and fruit smooth. 



7. Cereus. Stem often long and erect, sometimes scandent ; branching, 

 ridged, or angular ; flowers from the sides of the stem ; calyx-tube elongated 

 and regular ; stamens free. 



8. Phyllocactds. Stem flattened, jointed, and notched ; flowers from 

 the sides, large, having long, thin tubes and a regular arrangement of the 

 petals. 



9. EPIPHYLLUM. Stem flattened, jointed ; joints short ; flowers from the 

 apices' of the joints ; calyx-tube short ; petals irregular, almost bilabiate. 



■Tribe II. — Calyx-tube not produced beyond the Ovary. Stem branching, 



10. RHIPSALIS. Stem thin and rounded, angular or flattened, bearing 

 tufts of hair when young ; flowers small ; petals spreading ; ovary smooth ; 

 fruit a small pea-like berry. 



11. Opuntia. Stem jointed, joints broad and fleshy, or rounded; spines 

 barbed ; flowers large ; fruit spinous, large, pear-like. 



12. PERESKIA. Stem woody, spiny, branching freely; leaves fleshy, large, 

 persistent ; flowers medium in size, in panicles on the ends of the branches. 



The above is a key to the genera on the plan of the most 

 recent botanical arrangement, but for horticultural purposes it is 

 necessary that the two genera, Echinopsis and Pilocereus, should 

 be kept up. They come next to the Cereus, and are distinguished 

 as follows : 



Echinopsis. Stem as in Echinocactus, but the flowers are produced low 

 down from the side of the stem, and the flower-tube is long and curved. 



Pilocereus. Stem tall, columnar, bearing long silky hairs as well as 

 spines ■ flowers in a head on the top of the stem, rarely produced. 



