EMBRYO, SEED AND CARPEL IN THE DATE. 163 



weeks after pollination. Area about the embryo as seen in transverse 

 section soon after the digestion of the cell walls is begun in a and a* ; 

 a, Crushed cells empty save of oil drops; a', Uncrushed cells like 

 those in a; b, Cells in which the protoplasm is being attacked and the 

 oil segregates; V , Thin-walled endosperm between the growing endos- 

 perm cells of 6 and those of c. 15a, The integuments and edge of 

 endosperm at about this time. As yet no special tannin cells have 

 appeared (cf. f. 31) ; o. i. Outer integument, i. i. Inner integument. 

 16, Thirteen weeks after pollination. For full explanation see p. 

 16a, Single endosperm cell in the course of secondary thickening taken 

 from the position in f. 16 indicated by the black square at x. 



Plate 17. — Phoenix dactylifera. 17, About (17 weeks after polling 

 tion) and 18, For full explanations of these figures see p. 142. The 

 tannin in the embryo at the age of figure 18 is shown by the dotting, 

 which is intended to indicate the areas of denser reaction only. 

 About 18-19 weeks after pollination. 18a, Camera lucida drawing to 

 show the distribution of oil globules in zones a and a 1 of figure 18, in 

 which the same is shown diagrammatically. The irregular particles 

 are protein. 19, Nearly mature embryo; a, Crushed cells (a, a r , f. 20) ; 

 6', Partially thickened cells (6' , in f. 20) ; c, Definitive endosperm. 20, 

 Detail of f. 19 through the endosperm next the embryo; a, Crushed 

 cells with minute oil droplets; a', Partially crushed cells with larger 

 oil droplets; &', Partially thickened cells with transverse secondary 

 walls, with large drops and the remains of the protoplasm. Definitive 

 endosperm to the right of b'. Deglet Noor. 21, Cells of definitive 

 endosperm which have arisen by secondary division of elongated cells 

 which have resisted digestion. 22, The same as 20 but in front of 

 the cotyledon, showing the final divisions of the endosperm cells and 

 the digestion of their contents. 23, Detail to show the position of the 

 secondary division walls in the endosperm which resists digestion. 

 a. Crushed cells, b" partly thickened cells with their walls at right 

 angles to the axes of the endosperm cells from which they arose. 24, 

 Haustorium and adjacent endosperm of seedling with extraseminal 

 portion 2 cm. long; a, Crushed walls, blue with iodine; 6, Crushed 

 walls, not blue with iodine; c, Cytatic digestion advanced, oil agglo- 

 merated; d, Cytatic digestion beginning, oil agglomerating, protein 

 digesting; e 9 unchanged endosperm. 25, A younger stage than 24, 

 showing the embryonic layer blue-reacting with iodine still intact. 

 Cytatic digestion has begun in front of the cotyledon. Dots in the 

 embryo indicate tannin; cross-hatching, starch. 



Plate 18. — Phoenix dactylifera. 26, Embryo and adjacent endo- 

 sperm showing the distribution of tannin. 11 weeks after pollina- 

 tion. 26a, Transverse section of the same seed as 26, showing the 

 areas in which the secondary thickening of the endosperm cells 

 has begun. Here tannin is abundant, as shown by the dots. 27-29, 

 Successively older stages showing the spread of the endosperm tissue 



