266 COMPENDIUM OF GENERAL BOTANY. 



the internode or in the remaining leaf, for such torsion would be 

 without a purpose. Further, the internode following does not 

 become twisted, as might be expected, because the new leaves are 

 already in the proper lateral position. The weight of the remaining 

 lower leaf does not suffice to explain this phenomenon, since the 

 growth-processes due to gravity would suffice to overcome the 

 weight of the remaining leaf. 



3. The following is another interesting result obtained by 

 Schwendener and Krabbe. Theoretically a leaf or flower needs, at 

 most, to turn upon its axis 180 in order to bring it in a favor- 

 able position for light, etc. Careful observations have, however, 

 shown that long stems may turn from 500 to 700, while the 

 organs concerned retain their chosen adaptive position. If, after 

 having acquired the necessary amount of torsion, the organ becomes 

 further twisted by processes of growth, it is found that the exces- 

 sive torsion is again undone in the upper part of the petiole or 

 peduncle. This is another interesting example showing that adapta- 

 bility may be revealed by physical-physiological investigations, and 

 that the teleological law is riot seriously shaken, as often happens to 

 the u biogenetic law " (HAECKEL). 



C. MOLECULAR ORGANIZATION OF PLANT-STRUCTURES. 

 (APPENDIX TO THE CHAPTER ON THE PHYSIOLOGY OF GROWTH.) 



The following German botanists have made a special study 

 of this difficult subject : MOHL, N. J. C. MULLER, WIESNER, 

 DIPPEL, VON HOHNEL, ZiMMERMANN, AMBRONN, and especially 

 NAGELI and SCHWENDENER ; among specialists in other fields, v. 

 EBNER. 



Some of the problems relating to this subject were touched 

 upon in the discussion of growth by intussusception (starch- 

 grains and cell-walls). The following statements are based 

 upon the results of the investigations of the authors mentioned. 



1. According to Nageli's micellar theory all bodies capable 

 of swelling (in botany we mean especially the starch-grains and 

 cell-walls) consist of micellce or aggregates of micellae. 1 During 



'According to Nageli, chemical molecules unite to form molecular masses of 

 higher order. If this molecular union takes place after a definite method (as, for 

 example, the union of a salt with water of crystallization) the resulting molecular 



