326 FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES III 



from d), and this is in contradiction to the optical result which proves 

 the outer portion of the layers to be less dense than their inner portion 

 (Fig. 1 5 6, p. 515). Therefore, an arrangement as indicated in e) would 

 better correspond to the optical behaviour of the grains. But then 

 the inner portion of the layers ought to be attacked first by ^-amylase. 

 This contradiction and the fact that no chemical polarity of the layers 

 has ever been observed, make a compromise probable as shown in f). 

 If the amylopectin molecules grow in both directions, the layer will 

 be chemically uniform. Further, branches running in opposite 

 directions may crystallize with each other (Fig. 163). Since in the 

 crystal lattice of cellulose the glucosan chains run also in opposite 

 directions, such a structure for starch is quite probable. The diagram 

 of Fig. 163 would allow of a mixed crystallization of amylose with 

 amylopectin and it shows how gaps may arise in the crystal lattice 

 of starch. Since the X-ray diagram is that of a fibre texture, the two 

 directions of the bifurcating chains cannot be crossed as in Fig. 163, 

 but must run almost parallel. 



Of all the theories so far developed for the structure of starch 

 grains, that propounded by A. Meyer (1895) comes nearest to the 

 views set forth here. Instead of his dendritic branching, however, we 

 assume that there is all-round interlinking, and that the dimensions 

 of the structure are reduced by some orders of magnitude to the 

 molecular. 



§ 2. Proteins 



a. Reserve Protein 



There is a fundamental difference between reserve proteins and 

 fibrous proteins. First and foremost, the reserve proteins are soluble 

 in water, dilute salt solutions, acids and alkalies, whereas the distin- 

 guishing feature of the frame substances is their pronounced in- 

 solubility. Reserve proteins frequently tend to crystallize if the solvent 

 is withdrawn in the proper way, as, for instance, by natural means in 

 the formation of aleurone granules owing to the drying up of vacuoles 

 in vegetable storage tissues. Polyhedral, crystallized corpuscles are 

 then formed, different, however, from real crystals in that they are 

 liable to swell and to take up stain. Nageli (1862) therefore called 

 them crystalloids. Notwithstanding the fact that the term "crystalloid" 

 was later applied by Graham in quite another, and etymologically 



