368 



CHLOROPLASTS AND CHROMOPLASTS 



CHAP. 14 



lation from experimental data. Hubert (1936) and Frey-Wyssling (1937, 

 1938) went beyond this, and attempted to give a detailed picture of the 

 arrangement of proteins, lipides and pigments in the chloroplasts. 

 Hubert suggested that chlorophyll molecules are attached by their hydro- 

 philic porphin "heads" to the protein layers, while their lipophilic 

 phytol "tails" are associated with lipide molecules; the entirely lipophilic 

 carotenoids are aligned between the lipide molecules. The resulting 

 picture is shown in figure 46. For reasons described below (page 376), 



iiiiii 



Fig. 46. — Hypothetical structure of chloroplasts according to Hubert. Rectangular 

 hatched bars represent hydrophilic groups, black bars — lipophilic groups; combination 

 of the two at right angles — chlorophyll molecules. The dumbbell-shaped structures 

 represent carotenoid molecules. Phospholipide molecules are indicated by tlie black 

 magnet-shaped structure attached to a hatched "handle." 



the lipide molecules are assumed to form pairs (by mutual esterification) ; 

 in this way, a protein layer can alternate with a double pigment-lipide 

 layer. Although the general character of the scheme of Hubert and 

 Frey-Wyssling appears plausible, its details are in no way proved and 

 the correctness of some of them is doubtful. We shall return to its 

 criticism on page 393 et seq. 



B. Composition of the Chloroplasts* 

 1. Separation and Total Quantity of Chloroplastic Matter 



The best known components of the chromoplasts are the pigments — 

 chlorophyll a, chlorophyll b, the phycobilins and the carotenoids. Their 

 properties will be described in chapters 15-20 of this volume and 21-24 



* Bibliography, page 396. 



