158 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



In all cases in which the total depression of freezing- 

 point is apportioned between electrolytes and non-electro- 

 lytes, it must be borne in mind that molecular proportions 

 are being considered, and not percentages by weight. 

 Furthermore, since electrolytes dissociate into at least two 

 ions, one molecular proportion (when in a dilute solution) 

 will produce twice as great a depression of freezing-point 

 as will a molecular proportion of a non-electrolyte. Again, 

 as the non-electrolytes consist in the main of mono- or di- 

 saccharides, having molecular weights of 180 and 342 

 respectively, whereas those of the electrolytes rarely exceed 

 the lower value, and as a rule are very much smaller, it is 

 clear that the percentage of electrolytes present by weight 

 in vegetable saps is in the majority of cases small compared 

 with that of non-electrolytes. 



CHANGES DURING THE RIPENING OF FRUITS. 

 For the fruit of Solatium laciniatum Mcolosi-Roncati 

 (1907), records a decrease in electrical conductivity, accom- 

 panied by a rise in osmotic pressure, according as maturity 

 is approached. In such respects, however, it is probable 

 that there is a great difference between fruits of various 

 species. 



TABLE XXXIX. 

 Solanum laciniatum. 



By far the most exhaustive cryoscopic researches upon 

 the ripening of fruits are those of Gavara. This author 



