202 STUDIES IN GENERAL PHYSIOLOGY 
nularia consists, for example, in simple hydrostatic effects. 
It would also be entirely useless to ask whether gravity is 
“the cause” of organization in Antennularia; naturally it is 
only one of the conditions determining organization. Under 
ordinary conditions, however, it is of paramount importance.' 
I add these remarks since it seems to me that the work 
of Pfliger on the effect of gravitation upon the division of 
cells is misunderstood in some of its points, and its value to 
the further development of physiological morphology is not 
appreciated as it should be. 
7. I shall in conclusion describe an experiment which I 
found in the botanical literature on the transformation of 
organs in plants through external forces. The reader may 
see from it that plants and animals are not essentially differ- 
ent in regard to the physiology of organization. 
I choose as an illustration Noll’s’ experiments on 
Bryopsis, which perhaps represent the most successful 
experiments ever made on the control of organization in 
plants through external forces. According to Noll, the 
so-called “leaf-barbs” (leaves) of Bryopsis mucosa arise near the 
tip of the upright stem. They are hollow tubes which spring from 
the main stem in two rows at an angle of about 45°. The roots 
arise from the lower part of the plant and grow away from the 
light into the ground, where they become attached to the particles 
of earth much as do the root hairs of the higher plants. The 
stems and leaves do not show this reaction to contact stimuli. 
The morphological differentiation of the organs seems to 
be much less marked in Bryopsis than in Antennularia, 
for, according to Noll, “by examination of a single organ 
doubt can easily arise as to whether the fragment originates 
from a root, a stem, or a leaf tubule.” In a normal Antennu- 
1In his Grundriss der Naturlehre, Macu defines cause and effect as follows: 
“Die auffallendste Bedingung der eingetretenen Veriinderung pflegt man die 
Ursache, die Veranderung selbst die Wirkung zu nennen.” 
2¥, Noun, Arbeiten des botanischen Instituts in Wurzburg, Vol. III (Leipzig, 
1888). 
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