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remained situated in the basal portion, whilst in the upper part 
growth quiekly diminished and wholly ceased. 
In order to observe well the growth of stems with individualised 
internodes, external conditions must be favourable: [ found that 
during the days on which the temperature was very low (an average 
of 10° ©.) the curve of rate of growth was almost a horizontal line 
with scarcely any maxima, and this was also the case with plants 
which at a higher temperature had a strongly undulating curve. 
All plants, which were found to have a lower rate of growth in 
or also under the nodal zone (to which class plants with intercalary 
growth also belong) possess complete nodes, that is to say, they 
show an external thickening round the stem at the point where a 
leaf is inserted. This may happen in plants with alternate leaves, 
but it always oecurs in plants with opposite leaves. 
On the other hand plants in which ill-defined nodes (“incomplete 
nodes”) are found, show in the growing region a single curve of 
growth rate and the nodal zones are not differentiated by a smaller rate. 
It is therefore seen from these observations that there is here a 
connection between phyllotaxis and the distribution of growth in 
the stem. 
With regard to the structure of the stem three theories are chiefly 
put forward. Next to the view that the leaves spring from the stem 
as independent organs (Strobilus theory) stands the phyton theory, 
which declares that the stem is composed of the basal parts of the 
leaves (GOETHE, GAUDICHAUD). CELAKOVSKY ') expressed this view in 
his caulome theory. 
A third opinion regards the interior of the stem as an axis round 
which there is a layer of leaflike origin. 
HormeistTeR regarded this development as ontogenetic, whilst 
Potonié?) thinks that it has taken place phylogenetically. The pith 
is according to Poronm the primeval caulome, round which origi- 
nally xylem and phloem have developed from “leaf feet” (phy llopodia). 
CELAKOVSKY’s theory as also those of HorMeIsTER and Poronimé, 
holds that the surface of the stem is composed of parts which belong 
to the leaves lying above it. Derpino ®) has called these parts “leaf 
feet” (phyllopodia). 
1) Grrakovsky L. T. 1901. Die Gliederung der Kaulome. Bot Zeitung 59er Jahrgang. 
2) Potonié H. 1912. Grundlinien der Pflanzen. Morphologie im Lichte der Palae- 
ontologie. Jena. 
3) Detpino. Atti della reale Universita di Genova. Vol IV, Parte Il, 1883. 
