453 



Studien uher die Protoplasmastromung bei den Characeen. Von Dr. 

 Georg Hormann. Jena. Gustav Fischer, 1898. 



Dr. Hormann gives us in this memoir the results of a number 

 of observations he has made upon rotation in the cells of the 

 CharacecB. So far as concerns the group in question, he accepts 

 De Vries's view that protoplasmic movement is a means whereby 

 mingling and transport of substauces is brought about. The effect 

 of streaming upon the development of organs, he maintains, con- 

 trary in part to A. Braun's conclusion, to be as follows : — that the 

 same relation holds in the case of both leaves and rhizoids, the 

 earliest developed cells in both cases being those arising at a point 

 towards which the stream is directed. Tiie direction of streaming 

 is held to be in close connection with nutrition : thus the stream 

 mounts along the outer (abaxial) side of the young leaf-cell, and by 

 this means nutritive matters are most quickly conveyed to that 

 part of the cell {i. e. the better illuminated) where they are 

 principally required ; as the leaf expands, the inner (axial) side of 

 the cell becomes in turn the better illuminated, and the cell being 

 by this time able to contribute its quota of elaborated matters, the 

 streaming favours transport of such matters out of the cell by the 

 shortest possible route. Moreover the direction of streaming — 

 from end to end — in the elongated cortical cells affords the most 

 favourable means for the products of katabolism to pass from the 

 internal cells and escape into the surrounding water. 



Velten's doctrine, that the rotating protoplasm always takes the 

 path of least resistance, is one which has found general acceptance. 

 Dr. Hormann, however, endeavours to show that this doctrine does 

 not apply to all cells of the Cliarace(E. In long cells, circular in 

 section, movement in the direction of least resistance should, he 

 argues, be circular movement and not longitudinal ; and this is 

 correct if the friction generated by contact between the moving and 

 the stationary protoplasm be alone taken into account. The point 

 overlooked by Dr. Hormann is the greater momentum acquired by a 

 rectilinear streaming as contrasted with tbat acquired by a curvi- 

 linear one ; and if this difference in momentum exceeds in amount 

 the extra retardation due to friction experienced by the stream 

 when flowing over angular portions of the cell, the path of least 

 resistance will lie from end to end of the cell. Moreover, we do 

 not see why there should be any necessary antagonism between 

 Velten's doctrine of " least resistance," and Dr. Hermann's of 

 " shortest way" ; for, though inclined to accept them both, we do not 

 think that the physiological advantage would be gained in any way 

 not involving the least expenditure of force. 



Dr. Hormann agrees with those who consider the movements of 

 such chlorophyll corpuscles as happen to fall into the stream to be 

 " active" movements, and he claims to have set the question 

 definitely at rest. But to us the two cases he cites do not seem at 

 all conclusive. The best one, namely, three rotating corpuscles 

 enclosed in a large clump of plasma, might be explained on the 

 supposition that a small quantity of protoplasm, not yet deprived 



