ipii] Francis Erncst Lloyd 35 



colloid, with which the tannin may unite, is made possible, while 

 the other processes are largely suspended. Following Prinsen- 

 Geerligs' work on the banana, Gore (1910) has shown that this may 

 occur in an atmosphere of carbon dioxid or of pure hydrogen.^^ 



This explanation harmonizes also with the facts obtained by 

 Bigelow, Gore and Howard (1906), which show that, during 

 ripening, the marc increases inversely as the tannin in their ex- 

 tracts decreased. There is, however, Httle or no decrease in the 

 absolute amount of tannin in the fruit, for its combination with the 

 associated colloid results in its conversion into a fomi which, being 

 unextractable (or only very slightly so) by alcohol or water, re- 

 mains in the marc. The marc itself also increases in bulk because 

 of the physical condition of the associated colloid with which the 

 tannin unites. In an unripe fruit, the associated colloid is extract- 

 able; in the ripe fruit it is not. 



During ripening, the tannin-mass contains a decreasing amount 

 of water. I have used the word dehydration (Lloyd, 191 1) to 

 describe this change, but I think that while graphic, it may not 

 express the truth except in a relative sense. The reduced power 

 of swelling may be due alone to an increase in the amount of colloid 

 which, as fast as formed, unites with the free tannin, or because 

 the complex thus formed has less capacity for Imbibition. That 

 there is an actual increase there seems to be no doubt, from the 

 facts afforded by the study of abnormal tannin-cells, which, for 

 some reason, have died in situ. Such cells become red or brown 

 in color, and have been observed by Aso (through Howard, 1906) 

 and by Howard (1906), but I believe, wrongly interpreted. On 

 exposure to air, the tannin-cells which are normal take on the same 

 red coloration. There is, therefore, nothing peculiar to these cells 

 in the color. This is rather in the form of the tannin-mass, which 

 in these dead cells, shows much greater amount of shrinkage, as 

 is shown by the more extensive superficial pitting in those cells 

 which have died in a quite immature condition of the fruit. This 

 shrinkage is a measure of the amount of colloidal material, or, if 

 one chooses to put it in another form, of the amount of water in it. 



" Communicated to me by Mr. Gore during a conversation with him. 



