846 
MECHANICS OF GROWTH. 
JlUium Porriim and of Allium Cepa the growth is basal. The position and the form 
of the geotropic curvature is therefore different in the two cases. 
The length of the growing region, when fully developed parts already exist, is 
greatest at a certain time, after which it diminishes as the stem gradually approaches 
its complete development, and finally disappears. The following measurements were 
made whilst growth was still active and the growing region of considerable extent. 
The length of the growing region behind the bud was in 
Fritillaria imferialis 
7-9 ctm. 
Allium Porrum 
about 40 
in one internode 
Allium Cepa 
30 
" ( 
, of the scape. 
Allium atropurpureum 
50 
Cephalaria procera 
35 
(3 internodes). 
Polygonum Sieboldi 
15 
» 
(4-5 internodes). 
Asparagus asper 
20 
J) 
(numerous internodes). 
Valeriana Phu 
25 
3J 
(4 internodes). 
Dipsacus Fullonum 
40 
J) 
(3-4 internodes). 
The measurement of portions of equal length (of one or of five ctm.) shows that 
the growth of each such portion is greater the more distant the portion measured is 
from the terminal bud, or, in the case of basal growth, from the base. At a certain 
distance from the apex (or the base) the maximum occurs ; beyond this distance the 
growth of each portion diminishes until it altogether ceases at the limit of the growing 
region. The form of the geotropic curvature and its modifications essentially depend 
upon these conditions. In these particulars stems which consist of numerous internodes 
but without w^ell-defined nodes {Asparagus) resemble long single internodes, such as 
the scapes of the various species of Allium. If however the stem is distinctly articulate, 
a curve of fractional growth may be obtained from each internode, which rises as we 
pass from its lower end until a maximum is reached, and then sinks as we pass towards 
its upper end. The node itself ceases to grow in length at an early period. As the 
result of this, the geotropic curvature of the whole stem is interrupted at the nodes, 
and the quickly-growing central portions of the internodes describe sharper curves. 
With the exception of this peculiarity, an articulate stem behaves generally in the 
manner above described with reference to a long scape consisting of a single internode. 
Finally, it is to be noted that each transverse zone of a growing stem grows at first 
slowly, then more rapidly until a maximum rapidity is attained, and then more slowly 
until growth ceases altogether. This also determines the form of the geotropic 
curvature. 
Those portions of a stem which have ceased to grow and which are incapable of 
renewed growth in consequence of a change of position (see what is said below about 
the nodes of the haulms of Grasses) will not assume an erect position when placed 
horizontally or obliquely. Only those portions of a stem laid horizontally or obliquely 
take part in the assumption of an erect position which are growing (as in the down- 
ward curvature of the root), and this in proportion to the phase of their growth, their 
thickness, rigidity, etc. This curvature is a consequence of a modification of the growth 
in length of the stem produced by its abnormal position, of such a nature that the 
growth of the under side is more rapid and that of the upper side less rapid than that 
of the stem in the erect position. In quickly-growing parts the upper side evidently 
increases in length when the geotropic curvature is taking place, but in older more 
slowly growing parts the length of the upper side does not increase, and it may even 
become a little shorter if the curvature is very sharp, whilst the lower side elongates 
considerably. These statements can be easily verified by direct measurement of thick 
firm stems before and after the curvature has taken place. It is obvious that the 
convex side of a curved stem must be longer than the concave, but the question as 
to whether or not the growth of the concave side is slower and that of the convex 
