EMBRYO, SEED AND CARPEL IN THE DATE. 133 



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periphery. I have found a relatively small amount of tannin 

 present even as late as October 8, in Deglet Noor material 

 pollinated on March 28. Frequently the disappearance of 

 the tannin is even in rate throughout the whole mass of the 

 endosperm, but one more often observes that it is at different 

 rates in different parts. In some instances (f. 28, 30), and 

 these are particularly instructive, the tannin remains longer 

 in certain sectors, having their vertices at the line of fusion 

 marking the obliteration of the endosperm utriculum, than 

 in others. The wedge-shaped areas (f. 28, 30) thus made 

 conspicuous, reach quite to the outermost layer of the endo- 

 sperm, and their superior tannin content is quite evident to 

 the unaided eye. In other cases, similar but irregular areas 

 occur, sometimes centrally placed and showing a radial dis- 

 position, or it may be less definite relations. On the whole 

 the tannin is retained rather longer in the general region of 

 the raphe than elsewhere, thus suggesting a movement of the 

 material concerned from this part of the ovule into the endo- 

 sperm. The last evidences of tannin are to be seen in the 

 outermost, peripheral endosperm cells, w T hich are the last 

 to take on their definitive character. These are at this time 

 passing from an obliquely distorted condition, due to 



shearing pressures exerted by the endosperm on the one 

 side and by the integuments on the other. With further 

 growth they finally attain a radial disposition, and the tan- 

 nin content entirely disappears, save in isolated positions. 

 The mature endosperm shows very little tannin, and this 

 is confined to irregular sulci, caused by uneven rates of 

 growth and the consequent tangential crushing of peri- 

 pheral portions of endosperm which are unable to thicken 

 their walls, and to adjust themselves finally to the sur- 

 rounding tissues. The minute quantity of tannin found 



i 



by Pond (1906, p. 74) is probably to be explained by this 

 circumstance, though a partial explanation may be had in 

 the incomplete eradication of tannin elsewhere. 



From the circumstance that there are no special tannin 

 cells in the endosperm at maturity, we must conclude either 



that it disappears as the results of chemical change or that 



