406 BOTANICAL GAZETTE [JUNE 
invertase: testing various portions of the date for inverting power, 
and comparative analyses of the various parts. Suitable materials 
for carrying on these lines of work were exhausted this year before a 
fair start could be made. It is our expectation to continue this 
phase of the work. Preliminary tests by the first method—dividing 
the date transversely into blossom third, middle third, and stem third; 
and concentrically into three parts, the outer shell down to the tannin 
layer, the tannin layer, and the inner portion—failed to give trust- 
worthy results. 
The physiological function of the tannin is little understood. 
Whatever else it may do, it efficiently protects the fruit from animal 
ravages and permits it to mature its seed, as has been demonstrated 
in the Tempe orchard this year.3° The loss of astringency on ripening 
was formerly believed to mark the conversion of tannin into sugar, 
but it was found that in the persimmon?’ the tannin only becomes 
insoluble. This has been found by THoRNBER®® and the writer to be 
true of the date also. Stape considered the tannin present as 
glucoside which was in some way split up, the tannin being oxydized 
by an oxydase; and in fact some experiments in which the loss of 
astringency and softening appeared to have been hastened by the use 
of manganese salts gave some ground for this opinion. This was 
further supported by the observations of TicHomrrow.3® Even if 
true, the tannin or tannin-glucoside is so small in amount that it could 
not appreciably interfere in the carbohydrate relation. Many other 
quantitatively minor changes undoubtedly take place at the time of 
softening, among others the change in the behavior of the invertase 
toward solvents, which I hope to discuss at length in some future 
paper. 
There remains at least one other way in which cane sugar dates 
differ chemically from invert sugar dates. E. E. Frer, who assisted 
in these experiments, noticed and called my attention to the fact that 
sugar solutions to which cane sugar date extracts had been added 
developed a pink tint. This was more pronounced and developed 
36 Annual Report, Ariz. Agric. Exp. Sta. 17: 164. 
27 BIGELOW, Gore, and Howarp, Joc. cit. 
38 Loc. cit. 
39 Compt. Rend. 39:305. 1904; through notes of H. B. SLADE. 
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