and visible characters, in which the
origin and function of the determinants is presented; (5) Variety, race,
"nutrition variety," heredity and variation; (6) Criticism of the
Darwinian theory of natural selection, in which the author urges seven
objections to that theory; (7) Laws of evolution of the plant kingdom;
(8) Alternation of generations from the standpoint of phylogeny; (9)
Morphology and classification as phylogenetic sciences; (10) A
comprehensive summary of the whole work, a translation of which is
given in the foregoing pages.

In the first part of the work Naegeli sets forth his micellar theory of
the structure of organized bodies. This is one of his most important
contributions to science. Until recent years it has been the only theory
given in botanical text-books. At the present time its only competitor
is Strasburger's lamellar theory, and even this has not superseded
Naegeli's work to any great degree.

The reader who may not be familiar with the micellar theory will find
the general idea from the following brief sketch adapted from Vines's
_Plant Physiology_:

"Naegeli's micellar theory was developed from his study of
organized bodies, especially of cell walls and starch grains.
From the behavior of organized substance toward water absorbed
by it, he concluded that water does not penetrate into the
micellae, but only among them, thus merely separating them more
from each other. He reasoned that if water should penetrate into
the micella, its structure would be disintegrated. Hence he
argued that organized bodies consist of solid micellae, which,
with their respective films of water, are held together by: (1)
The attraction of the micellae for each other, which varies
inversely as the square of the distance. (2) The attraction of
the micellae for water, which varies inversely as some higher
power of the distance. (3) The force which holds together the
ultimate chemical molecules of which each micella consists.

"Since the swelling up of organized bodies does not take place
equally in all three dimensions of space, and on account of
their double refraction, Naegeli inferred that in form the
micellae are crystals, probably parallelopipedal, with
rectangular or rhomboidal bases."

The law that "bodies attract each other with a force which varies
inversely as the square of the distance," has been proven only in its
applica