108 



a great treasure of positive observations : it is a work the more 

 desired as we have recently obtained so complete a monograph 

 of this family. The Cactece are, says the author, provided 

 either with true leaves (Peireskia) or their rudiments (Opuntia, 

 Rhipsalis, Epiphyllum, Hariota,Lepismium, many Cerei), or are 

 actually leafless (Mammillaria, Melocactus, Echinocactus, the 

 rest of the Cerei). From the axes of the leaves or, when these 

 are wanting, from those places, where according to the laws 

 of the arrangement of leaves they would be situated, bundles 

 of thorns of various forms are developed, which may, accord- 

 ing to analogy, be regarded as buds, and the thorns as thorny 

 scales. In the Peireskice, in which alone true leaves occur, the 

 petiole is separated from the leaf and is regularly thrown off. 

 In the Opuntice the leaves are merely round, unarticulated, 

 pointed or obtuse formations, properly speaking only rudi- 

 ments of leaves, which gradually dry. In Rhipsalis, Epiphyl- 

 lum y &c., they are only small adpressed scales, ciliated at the 

 border, which also subsequently dry. The development of the 

 pulvinus stands in an inverse relation to the occurrence of 

 leaves in the Cactete : thus in the Peireskice it is almost im- 

 perceptible, but appears prominently where there is no forma- 

 tion of leaf. 



The thorns or bundles of spines are situated in, or some- 

 what above the axis of the leaves, whether these occur or not : 

 in the latter case it will be evident from the spiral arrange- 

 ment peculiar to the leaves. It may also distinctly be ob- 

 served on the skeleton of the Opuntice that the ligneous 

 bundles proceed to the thorn-bundles just as they do to the 

 buds in other plants. Attention is also drawn to Barleria 

 lupulina, one of the Acanthaceae, where similar thorny buds 

 occur together with the usual ones. Numerous similar cases 

 however occur among the Syngenesista. 



The thorns of the Cactece, which consequently must be re- 

 garded as metamorphosed bracts, are never hollow, but always 

 solid and of a firm corneous texture. They are smooth or 

 finely and softly haired. In Opuntia exuviata, tunicata, &c., the 

 upper cellular layer disengages itself, beginning at the basis of 

 the thorn, and then covers it as a sheath, which is easily drawn 

 off. The thorns frequently grow for many years, each time 

 advancing somewhat at the base, when the new-grown portion 



