2o6 



FINE-STRUCTURE OF PROTOPLASM 



II 



belonging to the cytoplasm or as a membrane of the vacuole. From 

 the point of view of molecular morphology this point of contention 

 can be decided in the following way (Fig. ii8). 



As a resuh of the accumulation of Hpids, the latter are no longer 

 in equilibrium with the protein framework. Their molecular forces 



o O O o o 

 ^o o o o o 

 „ ° o o o 

 o o O o 

 ° o o 



}. Cytoplasm 



' Tonoplast skin 



Va c u ole 



°; 



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 iiUAiiiiiUA 



???????????? 

 UiiiiiiiiAl 



O Oo00o°0 



Fig. 1 1 8. Scheme of the submicroscopic structure of the tonoplast membrane, consisting 



of polar lipid molecules (cf. Fig. 115, p. 199). Hydrophylic groups white, lipid chains 



black, water molecules small circles, a) Bimolecular, b) polymolecular film. 



cause them to arrange themselves, turning their hydrophilic poles 

 towards the hydrophilic inner plasm, the lipophilic ones towards the 

 vacuole. As ascertained in the case of Allium (Fig. 46, p. 55), the 

 inner part of the vacuole consists of a hydrophilic liquid; the outer 

 boundary, on the contrary, has a more lipophilic nature. In comparison 

 with the cytoplasm, therefore, the lipid molecules in the vacuole must 

 be arranged in exactly the reverse order. The result is that the bound- 

 ary region of cytoplasm and vacuole consists of a lipid layer which on 

 either side, without any sharp transition, gradually changes into 

 hydrophilic regions. The boundary membrane will therefore consist 

 of molecular double layers. 



It is evidently difficult to say which part of this lipid layer belongs 

 to the cytoplasm and which to the vacuole surface. The only criterion 

 would be to determine to what extent the cytoplasmic protein frame- 

 work penetrates into this layer. Since, however, this cannot be decided 

 by vital staining, we must content ourselves v/ith the fact that the 

 boundary between the two cytological parts cannot be accurately 

 determined. 



