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. 1 



I add these remarks since it seems to me that the work 

 of Pfltiger 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. 



1 choose as an illustration Noll's 2 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- 



iln his Grundriss der Naturlehre, MACH defines cause and effect as follows: 

 "Die auffallendste Bedingung der eingetretenen Veranderung pflegt man die 

 Ursache, die Veranderung selbst die Wirkung zu nennen." 



2 F. NOLL, Arbeiten des botanischen Instituts in Wilrzburg, Vol. Ill (Leipzig, 

 1888). 



