492 PROF. PERCY GROOM ON THE 
produced during one vegetative season, and constituting either the main 
stem of a herb or the year's long-shoot of a woody plant, show a regular 
rise in length, succeeded by a fall This rhythm 1s inherent, and occurs 
whether the stem bears its strongest branches at the base, middle. or apex. 
(Some arboreous species display in their year's shoot two internodal 
* eycles ” : this is associated with the production of a second crop of leaves 
in one season.) 
2. [n trees the strongest and largest lateral buds, destined to produce the 
strongest branches, are usually inserted nearest to the top of the year's 
shoot, a climax being reached in such types as the pines, where all the 
lateral buds responsible for the production of long-shoots form a false whorl 
immediately beneath the top of the year’s shoot. In shrubs the strongest 
buds are usually inserted near the base of the year's shoot. Whilst in some 
trees, especially those with a shrubby or weeping tendency, the insertion of 
the strongest buds is apt to be intermediate between the extremes just 
denoted. 
3. Just as the successive internodes wax and usually wane in size on the 
year’s shoot so likewise do the leaves on this, an extreme in the reduction 
being reached in the scale-clad terminal buds of woody plants. It should be 
noted that the curves representing the dimensions of the successive leaves 
and internodes of a year’s shoot do not necessarily synchronize as regards 
phase. These changes in the dimensions and shapes of the successive leaves 
result in more or less distinct corresponding differences in their scars. 
The question arises: “ Do the Calamite-stems conform in all three 
respects with the woody stems of dicotyledons?” In the sueceeding? para- 
graphs are described the results of the three types of tests applied to 
those specimens of Calamite-stems that have sufficiently numerous internodes 
and sufficiently distinct scars of buds or branches and leaves. And, to 
antieipate, it may be stated that the conclusion to be drawn from the 
available statisties is that these stronglv suggest that each cycle in the 
characteristic rhythm in Calamite-stems corresponds to one season's growth 
in length. 
I. Regularity of the Period (Cycle) of Internodes of Calamite-stems. 
In the following Tables, each re- 
Curve I. . 
ferring to one stem only, the suc- 
Calamites Schützei : measurements are 
in centimetres. cessive internodes are ranged from 
left to right in horizontal series, each 
complete horizontal line representing 
one assumed cycle and one season's 
growth in length. B denotes the 
position of the branches. Thus the 
vertical series ina Table represent in 
a sense homologous internodes. 
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