210 FINE-STRUCTURE OF PROTOPLASM II 



phological principle of the unsaturated five-membered ring seems to 

 be particularly important. We do not know how this ring fits into 

 the protoplasmic structure, but it must possess a specific kind of 

 stimulating activity, adapted to a certain configuration of the cyto- 

 plasm frame. It cannot be accidental that histidine (Fig. 120, V), the 

 specific stimulant to protoplasmic flow (Fitting, 1927, 1936), should 

 also show the unsaturated five-membered ring, although admittedly 

 with two double bonds. 



Even the double bond alone is capable of initiating some of the 

 reactions mentioned, for traces of ethylene (Fig. 120, VI) cause typical 

 epinastic curvature of leaves (which are even used as test reactions, 

 Denny, 1935), and give rise to the formation of adventitious roots 

 in the presence of a sufficient amount of auxin (Michener, 1935)- 

 For the initiation of cell elongation, however, the acid group too 

 seems to be required. At the moment, molecular morphology is unable 

 to account for the fact that the combination of a double bond and 

 an acidic group has to be realized by means of some five- or six- 

 membered ring. 



§ 2. Nucleus 



a. Molecular Constituents of the Nucleus 



The isolation of sufficient quantities of substances from the cell 

 nucleus for chemical purposes meets with great difficulties, and so far 

 it has been possible to carry out a thorough chemical analysis only 

 in special cases, in particular in the case of the sperm nuclei of fishes, 

 where extremely interesting results have been obtained. The following 

 account therefore refers primarily to fish sperm, but a generalization 

 applying to the chemistry of other nuclei on the strength of micro- 

 chemical analogies is permissible, howbeit with due caution. The 

 nuclear substances designated as nucleoproteins can be separated into 

 two components, viz., into proteins on the one hand and phosphor- 

 containing nucleic acids on the other. Other compounds such as 

 lipids (Hirschler, 1942) are present in insignificant quantities. 

 ScHMiEDEBERG (KiESEL, 1930) finds fot the Sperm heads of salmon: 



nucleic acid . . . . 60.50% by weight 

 protamines . . . . 35.56% ,, ,, 

 rest, with 0.12% Fe 3.94% » » 



