igii] Francis Ernest Lloyd 9 



the course of ripening, there is a decrease in tannin and a corre- 

 sponding increase in marc. That the marc of ripe fruits contains 

 tannin, and that this is insoluble, appears from their Statement that 

 it may be extracted from the marc only on warming with dilute 

 mineral acid. In attempting a theoretical explanation of the in- 

 solubility of the tannin, these authors found themselves compelled 

 to say that the tannin " either combines with some substance of low 

 molecular weight . . . or is converted into an insoluble form by a 

 change in the nature of the tannin itself." The former alternative 

 they discarded as improbable, and adopted the latter, their position 

 receiving support from Howard independently on microchemical 

 grounds. I have already called in question the logical validity of 

 this explanation. To say that the tannin becomes insoluble, it ap- 

 pears to me, is to State an unquestioned fact which needs explana- 

 tion; to explain the change from solubility to insolubility by postu- 

 lating a change in the nature of the tannin itself (which has not 

 been shown to occur), does no more than to introduce the difficulty 

 of explaining this change. Vinson (1910), treating of the date, be- 

 lieves that enzymic action intervenes. He bases his views on the 

 inhibiting effect of heat on the change in question. Ripening with 

 loss of astringency, he says, follows treatment such as to destroy 

 protoplasm, but not enzymes ; after temperatures sufficient to 

 destroy the latter, astringency is not lost. Assuming the correct- 

 ness of this conclusion, I would offer as an accessory view of ten- 

 tative value that the enzyme invoked by Vinson has to do with the 

 formation of a colloid with which the tannin may unite. 



In its bearing on the present paper, it is important to note that, 

 whatever the stage of ripening^ the fixation of tannin is not usually 

 complete. Bigelow, Gore and Howard (1906) record the finding 

 of traces of soluble tannin in all cases, at all stages of ripening 

 studied by them. I, also, have found this to be true, but it will be 

 understood, as indeed is the case, that the amount is not sufficient 

 for detection as astringency, perhaps for quantitative reasons 

 alone but probably, also, because of the nature of this free tannin. 

 I have further found that at a stage when the fruit may still by 

 courtesy be regarded as palatable, the amount of soluble tannin may 



" The term " ripening " is not restricted in this paper to the changes leading 

 to edibility, but includes all later autolytic changes. 



