52 
A. II. Church. 
come under this rule. The terms ‘genetic-spiral,’ ‘divergence-angle,’ 
‘orthostichies,’ ‘parastichies,’ were introduced, and these still 
comprise the familiar terminology of the text-hook; but the spiral 
remained the same helix proposed by Bonnet. It is not, however, 
always pointed out in these text-books that descriptive morphology 
was here really still concerned solely with adult structures, the 
definition of an adult part being that it has stopped growing. It 
refers that is to say, to a mathematically ideal construction which 
quite possibly is never absolutely attained in the living plant’ 
although on adult cylindrical axes, as in the case of some Cacti the 
approximation is perfect to the eye, and even within the error of 
verv small measurements. 
Bonnet's spiral thus only holds, and was intended only to hold 
as a mathematical conception for this very special case. A helix 
with parallel screw-thread demands equal members or members 
equally spaced; in such cases true orthostichies become possible in 
a spiral system. The elaborated spiral system of Schimper and 
Braun is thus mathematically perfect, as the representation of a 
special case of adult plant construction; and so long as the adult 
plant is considered the sole object worthy of scientific discussion 
this elegant and precise system of nomenclature will remain 
unrivalled for all descriptive purposes. It does not, however, 
explain anything, and something more than mere description has 
always been the aim of the new school of Botany, which may be 
dated from the time of Schleiden (1842), Hofmeister, Von Mohl, 
Nageli and Sachs. 
As the doctrine of Constancy of Species slowly gave way to 
theories of Evolution; and the leaven of such ideas as were 
presented in Goethe’s Theory of Metamorphosis of Leaves, and the 
philosophical discussions of growth, development and heredity by 
the eminent botanist and naturalist Lamarck, gradually permeated 
the scientific world ; the more intimate acquaintance with the 
minute structure of developing organs which led to the discovery of 
the growing substance of plants by Von Mohl, also produced a 
clearer conception of the plant body as a growing mechanism 
(Schleiden, Nageli). 
Just as the adult body was the theoretical ideal plant of the 
older morphologists, so a growing body became the type plant of the 
new morphologist, as seen in the growth of the members, growth of 
the axes, growth of the whole individual, its reproduction and the 
growth of the race; while the adult structures yielded place in 
