432 BOTANICAL GAZETTE [JUNE 
been able to find transitions between these spines and either leaves or 
emergences (except in the case of a few monstrosities which may have 
another meaning), nor have repeated experiments succeeded in making 
the spines return to leaves or emergences. Now, the cactus spines are 
immensely variable, becoming very big and hard on the one hand, or 
weak and small even to disappearance on the other, cylindrical and 
erect to ribbon-like and contorted, plain or variously ornamented, 
smooth or beautifully plumed or fringed, curved into hooks useful for 
climbing, or altered entirely into nectaries. But, throughout all of 
these variations it is distinctly and unquestionably a spine, an anatomi- 
cal spine that is varying, and not a disguised leaf or emergence. We 
must conclude from all these grounds that the cactus spine has attained 
to full morphological membership, is itself a member, a center of modi- 
fication and metamorphosis. The mamillae, or tubercles, in the same 
family, originate by a union of the leaf-base and its axillary bud, but 
the identity of these two parts becomes completely lost in the new 
identity of the tubercle, which becomes a member and acts as such 
through many genera. The ribs in Cactaceae arise by the running 
together of vertical lines of tubercles; once formed, however, they pay 
little attention to their mode of origin but proceed to act as independ- 
ent members, as one may clearly see when he considers their perfor- 
mances (particularly their independent increase or reduction in 
number) in the development of the cladophylls of Phyllocactus 
already cited in this paper. In some genera, however, particularly 
Echinocactus, the ribs have not attained to full independence, for they 
occasionally revert to lines of tubercles. But we need not go so far afield 
for our illustrations of the attainment of independent membership, for 
the members commonly accepted by the idealistic system (root, stem, 
and leaf) illustrate it perfectly. Most of us no doubt believe that the 
present-day foliage leaf and stem arose through the sterilization of 
sporogenous tissue in a primitive very simple sporophyte ; but whether 
we believe it or not does not matter for our present purpose, for we must 
believe, if we accept evolution at all, that leaf and stem have become 
specialized out of a simpler structure which did not show those dis- 
tinct parts? All morphologists accept the foliage leaf and its stem as 
of full morphological membership and independence, to such a degree 
indeed that they stand in most minds as the very types of morphologi- 
cal members. Now, in their case, even the idealists never attempt to 
interpret their morphological behavior in the light of the nature they 

