435 
the Adventitious Leaves of Cyclamen . 
together, their traces may become grouped more or less in a ring. No 
special morphological significance is attached to the form or course of the 
leaf-traces. 
On examining an adventitious leaf, the lamina of which had its back 
towards the tuber, it was found that the petiolar bundle was still reversed 
at the point of attachment of the petiole to the tuber. A partial rotation 
of the bundle, however, took place at once on entering the tuber. 
The leaves referred to so far are those produced on the uninjured 
surface of the tuber. Other adventitious leaves, however, had been formed 
on the cut surface of the tuber, but only in a small proportion of the speci- 
mens examined. Nothing specially noteworthy was observed in these 
leaves. Where they occurred near the central region of the cut surface, 
their vascular traces became attached to the bundles of the stele, not far 
below the cut ends of the latter, the traces having a very short and nearly 
vertical course. 
Probably a leaf-trace can be formed in the cortex of any part of the 
tuber, the necessary condition in any given region being that a young leaf- 
rudiment should first be formed there. 
No definite opinion has been obtained as to the nature of the stimulus 
requisite for the initiation of the leaf-trace in Cyclamen , but reference may 
be made to Simon’s conclusion regarding somewhat analogous phenomena 
observed by him in Achyranthes and other plants . 1 In Simon’s experiments 
a young stem was partially cut across transversely, so that some of the 
vascular bundles were severed, and observations were made on the develop- 
ment of new bundles, which were formed from parenchymatous tissue in 
such a manner as to connect the severed bundles above the cut either with 
uninjured bundles, or with severed bundles below the cut. The development 
of the new bundles began in parenchyma adjoining the cut ends of bundles 
above the incision (i. e. in tissue at first somewhat depleted of water 2 ), and 
proceeded towards bundles having a direct vascular connexion with the 
root, and consequently an efficient water-supply. Simon concludes, from 
the results of his experiments, that there is a stimulus depending on the 
distribution of water in the tissues, and draws a comparison between the 
reaction (of bundle development towards the water-supply) and the pheno- 
menon of hydrotropism. 
If one supposes the stimulus in Cyclamen to be likewise connected in 
some way with local scarcity of water, one must assume a degree of 
depletion of water in the cells adjoining the leaf-rudiment, at an early stage 
of the latter. This might possibly be due to increased cuticular transpiration 
1 Simon : Experimentelle Untersuchungen iiber die Entstehung von Gefassverbindungen. 
Festschr. deutsch. bot. Gesellsch., 1908, p. 364. See alscnKuster : Progressus Rei Botanicae, vol. ii, 
pp. 541-9; and Freundlich : Entwicklung u. Regeneration von Gefassbiindeln in Blattgebilden. 
Jahrb. f. wiss. Bot., vol. xlvi, 1909, p. 137. 
2 Owing to interruption of vascular supply of water from below; 
Gg 2 
