1895.] Present Problems in the Cactacee. 131 
forced to this position doubtless as a result of condensation 
of leaf-bases at the vegetative point. Leaf-base and axillary 
bud grow henceforth as one structure together and form the 
tubercle which attains its highest form in Mamillaria and 
Leuchtenbergia, and numbers of which merging together in 
vertical rows, sometimes with the cooperation of the stem 
physiologically replace the lost leaves, and varying in height 
and form allow of adaptive increase or decrease in spread of 
green surface, which is all in the xerophilously advantageous 
vertical direction. The spines are metamorphosed leaves, 
originating dorsiventrally on the sunken hair-protected axil- 
lary vegetative points, which may either be carried up entire 
by the growth of the tubercles and come to stand finally on 
their tips, as in Opuntia, Cereus, Echinopsis, Leuchtenber- 
gia, etc., or they may split into two parts as in some divis- 
ions of Echinocactus and Mamillaria, one part going up on 
the tubercle and producing spines, the other remaining 
behind in or near the axil to produce a flower or a branch. ® 
The flowers, produced rapidly during or at the close of the 
rainy season do not share the vicissitudes of the stem, and 
show no special adaptations to the dry climate. The ovary 
is deeply sunken in the flower-bearing stem, and the fruit, 
though often dry, is usually an edible berry, ensuring the best 
method of dispersal and conditions for germination in a dry 
climate. The seedlings are also succulent, with a spread of 
surface corresponding in a general way to that of the adult 
plants. 
I have elsewhere traced briefly the steps by which this 
knowledge has been won.* The only work upon the compara- 
tive anatomy of the order is Schleiden’s celebrated treatise 
of 1845,5 which despite some errors peculiar to that time, 
clearly outlined the essential features of the subject. Von 
Mohl studied their bundle-systems, and many later students 
have gone to them for special points, all of which may be 
traced in the work of DeBary,* since which little of import- 
ance has appeared, for the golden age of anatomy is not in 
: The full discussion of the points here outlined may be found in my paper, 
Beitrage zur Kenntniss der Morphologie und Biologie der Cacteen’’ in Flora, 
Erganzungsband, 1894. 
“ Flora, loc. cit. 
ror titles, etc., see Flora, loc. cit. 
Comparative Anatomy of Phanerogams and Ferns. 
