HYPOTHESES OF MOLECULAR STRUCTURE 81 



to be invisible. As a matter of fact micellae may attain a considerable size, while 

 any crystal may be regarded either as a micella or micellar complex. 



Even though the amount of swelling possible is not entirely dependent on the 

 form and size of the component micellae, nevertheless Nageli's conclusion that the 

 micellae of the starch-grain have their long axes radially arranged still holds good. 

 To this conclusion he was led by the study of the absorption of water by the grain, 

 and by the fact that the most marked swelling takes place in the tangential direction. 

 When boiled, starch swells greatly to form a paste, and probably not only does 

 a disorganization of the micellae ensue, but also a hydrolytic decomposition of 

 the polymeric molecules, which play so important a part throughout the group of 

 carbo-hydrates \ The phenomena of imbibition and swelling do not necessarily 

 postulate a growth by intussusception, and the arguments based by Nageli on the 

 supposed growth of the starch-grains by intussusception fall to the ground, for it 

 appears that starch-grains normally grow by apposition. 



Cell-walls, Many of Nageli's conclusions drawn from the striations shown 

 by cell-walls have proved to be erroneous, but nevertheless the numerous researches 

 conducted on the cell-wall have as yet brought no facts to light which are not in 

 accord with the micellar hypothesis. The power of swelling differently in different 

 directions might be due to the axes of the micellae being of different lengths, or to 

 other causes, such as, for example, to the component micellae being more firmly 

 attached to one another in one direction than in another. Such questions are 

 however not vital, but merely physical problems, which do not further concern us 

 except in so far as they affect vital phenomena. The study of the causes of the 

 torsion, thickening, shortening, splitting, &c., which may be produced by normal 

 (hygroscopic) swelling, as well as by abnormal and excessive swelling (Stein- 

 brinck's 'Ueberquellung'), is a task for the physicist and not for the physiologist. 

 If these phenomena are due to the particular shape or special arrangement of 

 the component micellae, it follows from the facts observed that one axis of each 

 micella must be perpendicular to, the other two parallel to, the surface of the cell- 

 wall, and at the same time often forming an acute angle with the long axis of the 

 cell 2 . 



It is difficult to hazard an opinion as to whether the particles, or dermatosomes 

 of Wiesner, into which the cell-wall separates when subjected to certain treatment, 

 such as in the process of so-called carbonization, are really preformed structures, 

 and whether if so, they represent micellae or micellar complexes, for similar 

 phenomena are also exhibited by artificially produced cell-walls 3 . 



Optical Characters. Although the optical appearances presented by organized 

 structures under polarized light were previously known, Nageli was the first to see 

 their real significance, and to found upon them conclusions as to molecular structure. 



1 See A. Meyer, I.e., p. 129. 



" Stein brinck (Zur Theorie der Flachenquellung, 1891) gives the literature. See also Nageli 

 und Schwendener, Mikroskop, 1877, 2. Aufl., p. 414; Schwendener, Sitzungsb. d. Berl. Aknd., 

 1887, Bd. xxxiv, p. 659. 



3 Wiesner, Elementarstructur, 1892; Pfeffer, Energetik, 1892, p. 253; Correns, Jahrb. f. wiss. 

 Bot., 1894, Bd. xxvi, p. 655 



PFEFFER G 



