

112 



MISSOUKI BOTANICAL GARDEN. 



The 



ib 



at this time is spherical in form, 60-75 



microns in diameter; at the time when the cavity is just 

 obliterated, the seed measures 2.5 mm. in diameter in the 

 transverse plane in which the embryo lies. The increase 

 from this time, to a transverse diameter of 8.5 mm., in the 

 ripe seed; and from a length of 8-9 mm. to 28-30 mm., is 



the period of maturation, 



speal 



d 



during 



and embryo. There is usually still more torsion, which 



mi 



the seed. The position is, however, variable and may occa- 

 sionally be quite abnormal. From the circular embryonic 

 area, visible on the outside of the seed, a slender line may 

 be traced downward. This is the evidence of the torsion, 

 and is the anatomical indication of the micropyle. 



Stage IV. Close of the Third Period. 



Carpel (f. 32, 33). The definitive epidermis, 15 microns 

 deep, is heavily cutinized, the cuticle 4 microns thick. The 

 cells are nearly isodiametric and straight walled. There 

 are occasional stomata, each supported by four or five acces- 

 sory cells. Beneath the epidermis is a thin layer of paren- 

 chyma 45 microns thick, of four to five layers of tannin 

 cells, compressed radially. Within this layer again is the 

 zone of stone cells, occupying a very irregular thickness 

 (60-120 microns) according to the position of the individual 

 cells. The longer ones are placed radially. It will be con- 

 venient to regard these tissues as constituting the exocarp. 

 The mesocarp is composed of very thin-walled parenchyma, 

 with here and there a raphide, or tannin idioplast, and 

 penetrated longitudinally by vascular strands. The midrib 

 of the carpel is marked by a median vascular strand, and 

 the suture by a dipping in of the layer of stone cells (f. 11). 

 The inner zone of the mesocarp is composed of more or 

 less crushed and disorganized parenchyma, which, in the 

 ripe fruit is conspicuous as loose, shining, fibrous masses 

 (the "rag"). These are only loosely attached to the endo- 

 carp, and constitute an irregular, poorly delimited zone which 



