200 FINE-STRUCTURE OF PROTOPLASM II 



accumulation comprises not only the plasmalemma but also visible 

 cytoplasmic layers, so that the presence of lipids causes a distinct 

 double refraction (Monroy, 1946). 



According to E. N. Harvey (1937) the cell surface is elastic; this, 

 according to model experiments, applies only to the surface of 

 solutions containing proteins, whereas lipidic drops of lecithin 

 (Harvey and Danielli, 1936) or of oil in living cells (E. N. Harvey, 

 1937) possess no surface elasticity! It follows from this that proteins 

 take part in the construction of the semi-permeable plasmalemma, 

 as I have already pointed out in earlier work (1935 a, p. 144). Un- 

 doubtedly the elastic properties of the cell surface are determined by 

 the network of proteins. The scheme with individuaU-:{ed spherical 

 protein molecules, which Danielli and Harvey (1935) believe to be 

 the structure of the phase boundary between oil inclusions and hydro- 

 philic cytoplasm, can only be valid for surfaces without elasticity ; the 

 elastic plasmalemma, rather, possesses a reticulate structure. Lehmann 

 (1950/52) has produced electron micrographs of the plasmalemma of 

 Amoeba proteus which show a meshwork of globular macromolecules 

 (fig. 104b, p. 160). This meshwork must be multilayered, since Mitchison 

 (1950a) finds the plasmalemma to show layer form birefringence. 



Probably this protein framework of the cvtoplasm is built more 

 densely into the oiater layers and changes gradually into a much looser 

 structure towards the inside. Accordingly, the cytoplasm in the egg 

 of the sea-urchin is liquid, and a similar conspicuous difference in 

 organization between ectoplasm and endoplasm seems to exist in 

 rhodophyta (Hofler, 1936b). At the phase boundary around the 

 vacuole the greater density of the framework and the accumulation 

 of lipids must occur again, causing a renewed resistance to diffusion 

 in this region. 



ScARTH (1942) has completed and improved the scheme of the fine- 

 structure of the cytoplasmic layers of plant cells suggested by me in 

 the first edition of this monograph (Fig. 115). Underneath the cell 

 wall lies the hyaline ectoplasm; its outer boundary is formed by the 

 plasmalemma rich in lipids. The endoplasm consists at its periphery 

 of plasma gel, with a network of protein filaments, and the central part 

 of plasma sol with more or less loosened junctions. It is intersected by 

 strands of higher density which, as kinoplasm, connect the ectoplasm 

 with the tonoplast. 



