78 IMBIBITION AND MOLECULAR STRUCTURE 



physical structure, to be regarded as micellae, they are undoubtedly 

 micellae which are capable of imbibing water and swelling, for chemical 

 changes take place in these pangenetic units, and chemical substances 

 penetrate to their interior. Indeed an internal molecular change is always 

 possible without the micellar structure being disorganized. This is the case 

 when, for example, a cellulose cell-wall is converted into nitro-cellulose, or 

 the latter reconverted into cellulose. 



Other conditions being equal, a greater amount of swelling will become 

 possible as the micellae are broken up into smaller and smaller micellae, and 

 the total micellar surface increased l . The amount of swelling is, however, 

 influenced by so many other factors that it must always remain uncertain 

 whether the different amount of water present in the successive layers of cell- 

 walls and starch-grains is merely due to the component micellae varying 

 in size in different layers. Nageli's ideas as to the progress and causes 

 of striation and stratification are partly based upon erroneous observations, 

 and hence the conclusions which he drew from the optical properties of 

 superposed lamellae containing varying amounts of water lose for the most 

 part their necessary basis of fact 2 . 



In the different layers of the starch-grain, amylose and amylodextrin are 

 present in unequal proportions s . Similarly it is uncertain whether the layers of 

 the cell-wall are chemically identical. Moreover other factors may modify the 

 power of swelling, such as the union of the micellae to form a skeletal framework, 

 or the occurrence of those infiltrations by which cell-walls are characteristically 

 modified to form cork and cuticle. 



Many organized bodies show a different capacity for swelling in one 

 direction than in another, and the velocity with which light is transmitted 

 may differ according to the way in which it traverses the organized substance, 

 being more rapid in one direction than another. From these facts Nageli 

 drew conclusions upon the mode of arrangement of the micellae, which are 

 not, however, necessarily correct ; for the amount of swelling is dependent 

 upon a variety of conditions ; while the study of the phenomena of polariza- 

 tion will not reveal the actual shape of the micellae, though it may indicate 

 that in particular cases they are anisotropous, and all arranged in the same 

 manner. On the other hand the isotropy of the protoplasm, does not 

 exclude the possibility of the component micellae being anisotropous and 

 crystalline but heterogeneously arranged, for the optical properties of 



Nageli, Starkekorner, 1858, pp. 333, 345. 



2 See Krabbe, Jahrb. f. wiss. Bot., 1887, Bd. xvill, p. 346; Correns, ibid., 1892, Bd. XXIII, 

 p. 254; Zimmermann, Beit rage xur Morphologic n. Physiologic, 1893, p. 302 ; as well as the works 

 here cited. 



3 A. Meyer, Unters. iiber d. Starkekorner, 1895, p. 2. On the behaviour of starch when boiled, 



1. C.. p. 1 2(). 



