260 THE PLANT WOELD. 



stigar, and he immediately pointed ont the great danger of in- 

 fering the chemical nature of a fruit from a limited number of 

 analyses, because climate, condition of season, and state of ma- 

 turity influence this factor so greatly. As a matter of fact these 

 differences were due to inherent phj'siological functions peculiar 

 to tlif variety itself and not to external causes. Thanks to the 

 U. S. I)e])artiiiont (tf Agricrdture, the more important ^■arieties 

 have been im])ortc'd from all the date growing regions of the 

 woi'ld and jdaccd in The Co-(»perative Date Orchard at Tempe, 

 Arizona, where they are easily accessible from the laboratory of 

 the Agricultural Exi^eriment Station at Tucson. 



The friiif of the date forms an almost ideal material for 

 rescarrli. Through it we see the main processes of fruit rijten- 

 ing as through a microscope. Phenomena wdiich in other fruits 

 are so slight as to be overlooked or considered as accidental, 

 here take on such proportions that they are unmistakable. Thus 

 the minute quantity of cane sugar which has been observed at 

 times in the cherry, certainly must ]ilay here the same physi- 

 ological role as the startling amount, 12% and over, which the 

 invert sugar date exhibits at a corresponding j)eriod. Further- 

 more the two types of dates exemplify the two types of non- 

 starchy fruit in general, the cane sugar and tlie invert sugar 

 ty])es. While the large amount of dry matter in the date has 

 been fax'oi'able to the study of the carlmhydrate relations, the 

 e\"en more btrlunate <li^tribution of tlie lannin has favored not 

 only the study of thai substance itself, but also of the enzymes. 



The tannin is doubly interesting because it can be observed 

 and studied so easilv. If vou cut a thin slice transversely 

 from a conunercial date and look throuiili it, you will observe 

 with the naked eye three zones; an outer transparent zone con 

 taining no tannin, a narrow reddish brown opaque zone cou 

 taining much tannin, and an iniuu- transparent portion again 

 free from tannin until it lilends into the so-called "rag." If 

 you now stir this jml]) with eonsi.deral)le water in a glass vessel, 

 allow it to rest a moment, and then observe the vessel from- 

 below, the contents of these opaque cells will appear on the 



