§36 The Botanical Gazette. [April, 
by the vegetative point forming it from a papilla homologous 
with those of the spines. If this be so, it is, as Goebel points 
out, additional evidence of the leaf-nature of the spines. Is it so? 
Are any intermediate forms between spines and leaf produced 
between the two, or is the transition sudden? Do these same 
axillary points, after producing the leaves, again produce 
spines? If so, the homology of the two would be clear. It 
is important to find a transition between tne splitting points 
of Peireskia and the non-splitting point often carried up by 
the tubercle in Opuntia. 
Epiphyllum shows phenomena in its flower and branch pro- 
duction which are best to be interpreted as due to a splitting 
of the axillary or the main points. Does this occur? In 
Rhipsalis a splitting of the axillary into several secondary 
points does take place. Splitting of the point is now known 
in Peireskia, Rhipsalis, Echinocactus, Mamillaria, Anhalo- 
nium. Does it occur in any other genera! f 
Leuchtenbergia principis is the most interesting species in 
the family. Its tubercles have become almost leaf-like, and 
its axillary points carried up upon their tips so that both spines 
(here papery) and flowers are produced there. This habit re- 
moves it from Mamillaria to that section of Echinocactus in 
which there is no splitting of the point, but the whole is 
carried up on the tubercle. Yet Leuchtenbergia is said to put 
out sprouts from the lower part of the stem. Whence do 
these come, from purely adventitious bud-formation, or 1 
reality is there a very early splitting of the point, the axillary 
part remaining a long time latent? The latter is very 1m- 
probable, but if it occurs it would restore Leuchtenbergia to 
relationship with Mamillaria. Are the tubercles shed like 
leaves? The development of this plant is unknown, and will 
give interesting results. 
The tubercles seem generally to act as assimilating organs, 
and their spread of green surface is readily controlled in 
amount by varying their height. In Opuntia, as Goebel has 
lately proven, }* the production of the tubercle is intimately 
dependent upon light, not forming at all upon sprouts grown 
in darkness. He has also shown elsewhere!* that when the 
tubercles are protected by a cephalium as in Cephalocereus, 
and in lesser degree in Melocactus, the union of leaf and ax- 
ite ene 
43Flora 80: 96-116. 1895. 
14Pflanzenbiologische Schilderungen 92, 93. 
