258 



FUNDAMENTALS OF FRUIT PRODUCTION 



are the pentosans, more particularly the water soluble pentosans. Evi- 

 dence is presented in the section on Water Relations to show that pentosans 

 of some sort are probably the compounds holding water in an adsorbed or 

 colloidal condition in plant tissues; this is confirmed by determinations of 

 Hooker, '*'* given in Table 14, which show a correlation between pentosan 

 content and hardiness. 



Table 14. 



-Pentosan Content of Plant Tissues in Terms of Fresh Weight^^ 

 (1920 Wood) 



This evidence supports the idea that pentosans largely determine the 

 water-retaining capacity of plant cells, though the particular compounds 

 concerned remain to be determined. 



Water Soluble Pentosans in Particular. — Water soluble pentosans, 

 such as gums or pectins, seem the most likely to act as water-retaining 

 substances. Studies by Rosa indicate that this is the case. Some of his 



Table 15. 



-Soluble and Insoluble Pentosans in Cabbage and Tomato 



{After Rosa'^') 



Total 

 pentosan 



Hot-water- 

 soluble pectin 



Insoluble 

 (by difference) 



Cabbage : 



Tender 



Hardy (dry grown) . . 



Hardy (by exposure) 

 Tomato: 



Tender 



Dry grown 



Exposed 



0.215 

 0.423 

 0.530 



0.693 

 0.720 

 0.682 



0.075 

 0.292 

 0.408 



0.070 

 0.071 

 0.071 



0.140 

 0.131 

 0.124 



0.623 

 0.649 

 0.611 



