EMBRYO, SEED AND CAKPEL IN THE DATE. 157 



bryo is very 



following pollination the growth 

 •iod is devoted to the growth of 1 



tissues of the ovule. The following period is marked especially by the 



reserve 



by the thickening of the walls of the endosperm cells. 



5. Starch has been found to play only a brief role in the basal por- 

 tion of the carpel and in the ovule. It is found in small and con- 

 tinually reduced quantities until the embryo is 6-7 weeks old. At this 

 time traces only are found in the integument between the micropyle 

 and the funicle. Subsequently none is found, till the embryo is about 

 17 weeks old, when it may appear in the radicle and in the cotyledon. 

 Its appearance in any position may be taken as indicating a temporary 

 reduction of growth activity in that place. This appears also to be 

 true both of starch and of oil in the early stages following germina- 

 tion. 



6. Certain tannins are important quantitatively and in their nutri- 

 tive relations. I have distinguished for convenience between aplastic 

 and plastic tannin. Aplastic tannin appears in particular cells and 

 remains there permanently. Plastic tannin undergoes translocation, 

 is consumed and disappears. This is taken as evidence of its nutri- 

 tive r61e. 



(a) Aplastic tannin in the carpel occurs in the hypodermis and in 

 the idioplasts. The latter form a well marked sub-hypodermal zone 

 which begins to be laid down at about the time of pollination. Tannin 

 as such does not migrate into these cells, nor into the hypodermal 

 tannin cells. There is therefore no evidence that during ripening 

 there is a segregation of tannin, as reported for certain other fruits. 



During ripening the tannin in these cells, as indeed all the aplastic 

 tannin, becomes insoluble, and hence tasteless. There is no evidence 

 forthcoming that this tannin is a glucoside and is oxidized, as tenta- 

 tively held by Slade 33 and for which a slight amount of evidence has 

 been mentioned by Vinson. Slade's view, however, is possibly applic- 



erm 



source of energy (vide infra) . 



The idioplasts form a morphological layer of cells which bends 

 toward the ovule in the sutural region, but is here discontinuous. 

 There is evidence here however of the presence of a small amount of 

 tannin of translocation which becomes more and more marked in 



.rpel 



ovule 



Aplastic tannin also occurs in a comparatively few, usually elon- 

 gated, elements scattered throughout the inner mesocarp, and in a 

 few cells also of the endocarp. 



33 See Vinson (1907) 



