36 MACDOUGAL— ACTION OF LIPOIDS IN GROWTH. 



character of the plasmatic membrane.^ Such an arrangement of 

 hpoids would be one which would permit the passage of both water- 

 soluble and fat-soluble substances into the cell. 



Czapek's notable contributions to this subject show that lipoids 

 are especially abvnidant in meristem and in nearly all cells in the 

 accretion stage of growth. Czapek places himself in the position of 

 considering the plasma as essentially a lipoidal structure.* Walter, 

 in confirmation of Biedermann, found that the plasmatic mass of 

 plants is not readily digested by proteoclastic enzymes until the lipoid, 

 which is held to be in a fine state of dispersion, is first extracted by 

 a fat solvent. He holds that his evidence is against the conclusion 

 that the lipoids are localized in a peripheral layer in the cell.^ 



The presence of lipoids in the cell colloids in the accretion stage 

 of growth would, it seems, almost inevitably result in their accumu- 

 lation in the peripheral portion of the plasmatic mass in accordance 

 with the laws of surface tension. That such a layer does exist was 

 concluded by Boas, who published a preliminary paper to this eflfect 

 in 1920 and his detailed observations upon which this conclusion was 

 reached in 1921. The experiments were based upon the known re- 

 actions of lecithin and cholesterin to neutral salts and to saponin. 

 Measurement of fermentation in yeasts and of the decolorization of 

 cells of higher plants are made the basis for the assertion that a 

 proteinaceous membrane in the cell is highly improbable, and that 

 lipoids are concerned in the exchanges of the cell with the medium.^ 

 Although this writer found that non-conductors in hypotonic solution 

 retarded the action of saponin on the supposed lipoidal layer, and that 

 hypertonic solutions of cane sugar, for example, accelerated it, the 



3 Hansteen-Cranner, B., "Beitrage zur Chemie und Physiologic der Zell- 

 wand und der plasmatischen Grenzschichten," Ber. d. Dcut. Bot. GeselL, ^7, 

 Hft. 8, 380-391, 1919. 



4 Czapek, F., " Zum Nachweise von Lipoiden in Pflanzenzellen," Ber. d. 

 Deut. Bot. Gesell, 37: 207-216, 1919. 



5 Walter, H., " Ein Beitrag zur Frage der chemischen Konstitution der 

 Protoplasma." Biochcm. Zeit., 122: 86-99, 1921. 



^ Boas, Fr., " Beitrage zur Kenntniss der Wirkung des Saponins auf die 

 Pflanzliche Zelle," Ber. d. Deut. Bot. Gesell, 38: 350^353, 1920. Also, " Unter- 

 suchungen ueber die Mitwirkung der Lipoide beim Stofif-Austausch der 

 Pflanzlichen Zell," Biochem. Zeit., 117: 166-214, 1921. 



