
901] BRIEFER ARTICLES 431 
development of metamorphoses, difference of degree passes over 
gradually into difference of kind. This principle, in my opinion 
the most fundamental in morphology, marks far more sharply than 
any other the difference between the two systems, for it is fundamental 
to the realistic, but inconsistent with the idealistic conception. It 
means that, as an organ gradually acquires a new function-structure, 
and the old function-structure is gradually lost, new powers of varia- 
tion, adaptation, etc., are acquired which become more and more inde- 
pendent of those formerly possessed by the organ, until finally the 
change may become so complete that the new organ not only acts 
itself quite independently of its old nature, but becomes a new start- 
ing point or center of metamorphosis, that is, it becomes a new mor- 
phological member. New metamorphoses, however, are not confined 
for their starting-point to the full members, but may originate from 
any of the points along the lines of gradation. Hence, not only may 
any Organ become a member, but the members grade into one another 
indefinitely and any of the gradations may act as members. This is 
in great contrast with the conception of the idealistic system as applied 
to the higher plants, for that conception not only limits the number 
of the members to a very few (at the extreme root, stem, leaf, plant 
hair, exclusive of the sporangia), but practically views these as sharply 
distinct, not recognizing intermediate transition from which new meta- 
morphoses may originate. In fact the idealistic morphology, while 
admitting the original evolutionary origin of its members, ignores 
evolution in their subsequent interrelationships ; it views its members 
much as species were viewed in pre-evolutionary times, while the real- 
istic system applies the idea of evolution throughout. The idealistic 
System views the morphological members much as a chemist does his 
elements, which may combine in many ways, but retain their identity 
throughout; the realistic system regards them more as a physicist does 
the colors of a spectrum, as a series of stages in a graded sequence of 
phenomena. 
As an example of an organ which has attained to full morphologi- 
cal membership and independence we may consider the spines in the 
Cactaceae. Research has shown much evidence for the belief that these 
structures have arisen by the metamorphosis of leaves; the only com- 
peting theory is that they are a form of ‘‘emergences;” no investiga- 
tor has ever seriously supposed they were anything else. Now, despite 
much long-continued observation and special search, no one has ever 
