The Submicroscopic Structure of Mannans 



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Fig. 1. Section througii a cell wail of date endosperm in its natural state. Magnification 5000. 



Fig. 2. Section through a swollen cell wall of date endosperm. Note the microfibrils between the swollen layers. 

 Magnification 20,000. 



Fig. 3. Date endosperm after Turmix and ultrasonic treatment before extraction of mannan A. Magnification 25,000. 



Fig. 4. Date endosperm after Turmix and ultrasonic treatment after extraction of mannan A. Magnification 25,000. 



endosperm of palm seeds there is available a material 

 which contains mannan, one of the most important 

 hemicelluloses. in a more or less pure form. An 

 attempt has therefore been made to gain some 

 knowledge of the submicroscopic structure of man- 

 nans by studying the endosperm of date seeds 

 {Phoenix dactylifera L.) and ivory nuts (Phytelephas 

 macrocarpa Ruiz et Pav.). 



Ludtke (4) has shown that there are two different 

 mannans in the cell walls of ivory nut, i.e. mannans 

 A and B which differ from each other by their 

 solubility in dilute alkali. The chemical structure 

 of the two mannans has been studied by Klages 

 (2, 3) and recently by Aspinall, Hirst and coworkers 

 ( I ). According to them these mannans are both com- 

 posed of two types of molecules, one having a 

 mannopyranose residue as non-reducing end group, 

 the other a galactopyranose residue. The two man- 

 nans should, according to Aspinall, differ from each 

 other only in their molecular size. By determination 

 of the end groups Aspinall has calculated a degree 

 of polymerization of 10-13 for mannan A and of 



39^0 for mannan B. It might however seem doubtful 

 that the difference between the two mannans should 

 lie in their molecular size only. In that case it would 

 be very difficult to understand why there should 

 not exist between the mannans A and B a series of 

 molecules with a degree of polymerization between 

 10 and 40. Moreover, this small difference in chain 

 length alone can hardly explain the very distinct 

 difference in the alkali solubility of the two man- 

 nans. 



In polarized light the cell walls of date and ivory 

 nut endosperm are highly birefringent. It does not 

 seem probable that this birefringence is caused only 

 by the 6 "„ cellulose (total carboh\drate content = 

 100 "o) that is found in the walls. Therefore the man- 

 nan forming about 90 "o of the cell walls must be 

 at least partly crystalline. With the aid of the polariz- 

 ing microscope the direction of the crystallites in the 

 thick central layer of the walls can be easily deter- 

 mined. In the date cells they run more or less per- 

 pendicularly to the cell axis and surround the pits 

 circularlv. 



