ORDER CRAS3ULACE.E, OR HOUSE-LEEK TRIBE. 441 



arillus, which gradually rises from the bottom of the ovule, and 

 at last envelops it completely. It will hereafter be seen that 

 the spice known as mace, is the arillus of the nutmeg. A spe- 

 cies of Passion-flower inhabiting the Isle of France is remarkable 

 for the narcotic properties of its root ; but it is not unlikely that 

 these are shared in some degree by others. 



609. Passing over several small orders, we come to that of 

 CRASSULACE^E, the House-leek tribe, which is chiefly interesting 

 as containing several British species of succulent plants, which 

 flourish under circumstances that would be fatal to almost all 

 others. They are found in the driest situations, where not a 

 blade of grass nor a particle of moss can grow, on naked rocks, 

 old walls, sandy hot plains, alternately exposed to the heaviest 

 dews of night, and to the fiercest rays of the noon-day sun. Soil 

 is to them a means of keeping them stationary, rather than a 

 source of nutriment. In this respect they resemble the Cacti 

 and other plants of tropical climates, which they represent in 

 more temperate regions. About half of the species known to 

 Botanists are natives of the Cape of Good Hope ; and nearly 

 half the remainder are European plants. Although they re- 

 semble the Cacti, and some other orders, in the succulent nature 

 of their stems and leaves, there is no other very close corre- 

 spondence between them. The number of parts in the flower is 

 subject to great variation. The calyx may consist of from three 

 to twenty sepals, which are united at the base. The petals are 

 equal in number to the sepals, and are inserted into the calyx ; 

 they are sometimes distinct, and sometimes cohere into a mono- 

 petalous corolla. The stamens are either equal in number to the 

 petals, alternating with them ; or are twice as many, in which 

 case those alternating with them are longer, and come to 

 maturity earlier, than the others. The carpels are equal in number 

 to the petals, and are opposite to them ; they are arranged in a 

 circle, and are more or less adherent in different species, each 

 having its own style and stigma. Every one contains several 

 ovules, which are arranged in two series along its internal edge, 

 where the dehiscence or opening usually takes place at the time 

 of maturity. The Sedums or Stonecrops, of which many species 



