EMBRYO, SEED AND CARPEL IN THE DATE. 113 



must properly be regarded as part of the mesocarp. The 

 endocarp is a definite, rather tough membrane (f. 34), com- 

 posed of the inner epidermis and more or less underlying 

 tissue of compact cells. This membrane adheres somewhat 

 firmly to the seed but splits readily longitudinally on 

 removal. 



Along the side of the placental ridge there are two parallel 

 strands of endocarp epidermis which are especially obvious 

 in chromic acid and ethyl nitrite material. They appear 

 to be differentiated on account of their anatomical relation 

 to the underlying placental tissue which is rich in tannin. 

 It is possible, therefore, that they represent transfusion areas, 

 where the tannin passes from the carpel into the ovule. 



Seed. The outer integument (f. 31). The epidermis is 

 completely sclerosed, having pitted walls. The cells are, on 

 the whole, elongated parallel to the axis of the seed, but at 

 the same time they show en face, a very great deal of torsion 

 and irregularity. There is an irregular hypoderm of more 

 or less similarly sclerosed cells, beneath which are thin- 

 walled tannin cells. It may be an expression of physiological 

 correlation that tannin is not to be found in the sclerosed 

 cells. The inner integument is somewhat difficult to delimit 

 sharply; it consists of at least two layers of cells, the outer 

 and inner epidermis, with usually one or two additional 

 layers of compressed cells between. The entire integumental 

 covering measures about 30 microns in thickness, but thick- 

 ens toward the raphe and above the embryo. 



Directly impinging upon this, and within it, is the thick- 

 walled endosperm. The outermost cells are very frequently 

 isodiametric, are thinner walled than those within, and have 

 few pores or none. The longer ones have pores at their 

 inner ends, or on the sides when unusually long. All the 

 cells radiate toward the morphological middle of the endos- 

 perm, which is marked by a mass of isodiametric, roughly 



spherical cells. 



The embryo is short and cylindrical in form, but is fre- 

 quently distorted longitudinally. It is placed at right angles 

 to its original position. The end toward the axis of the seed 



