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tial difference between the meristem-plasm of leaves on one hand 
and that of rhizomes and rootlets on the other. 
Hence there must be causes which in the cut leaf or in the 
rhizome bring about a division in the plasm for the formation of new 
prolifications and leaves, and since in cultures it is regularly observed: 
that new prolifications arise on the lighted side of the leaf, light 
certainly plays a part here. Undoubtedly, however, there are still 
other, internal, at present unknown, factors which cooperate in deter- 
mining the origin and place of origin of the prolifications. 
From the here briefly described observations we may infer that 
in the leaves of Cuulerpa a basipetal impulse is active, proceeding 
from every point of the leaf and revealing itself in two ways: 
1. in leaves, connected with rhizomes and rootlets, in the course 
of the “green” currents of protoplasm in the unwounded leaf as 
well as in the severely wounded leaves. 
2. in cut, vigorous leaves in the occurrence and course of the 
“white” currents of meristem-plasm which partly assemble at ‘the 
most basally situated place. It is this descending current which 
prepares the formation in that place of new rhizomes and rootlets. 
None of the observations, on the other hand, gave reason for 
assuming also the existence of a contrary, acropetal impulse, thus 
even not with the formation of leaves and prolifications. 
It proved possible, by certain lesions and by planting invertediy, 
to cause the formation of currents which developed contrary to the 
currents in the normal leaf. It could be proved however that this 
was not an inversion of the impulse itself, but that gravity or reflection 
by a wound caused a change in the direction of the current, whereas 
the basipetal impulse underwent no or hardly any change, and even 
then in any case only a very local one. 
The chief phenomena observed with Caulerpa remind us of obser- 
vations which have been known for a long time in higher plants. 
The consequences of annular wounds or of large transverse wounds 
in the bark-tissue of trees, the formation of much plasm-containing 
tissue (callus) above the wound, the frequent mortification of the 
tissue below the wound, the formation or sprouting of adventitious 
roots exclusively above the wound and in the very lowest place of 
the living bark-tissue, are, mutatis mutandis, evidently analogous. 
The same may be said of the formation of adventitious roots exclu- 
sively at the base of cut leaves of very many plants, of the regene- 
rative phenomena of the fruit-stalks of Marchantia, ete. 
The former phenomena were explained by the older physiologists 
