n6 



THE WHEAT PLANT 



appears as a protuberance from the posterior inner surface of the cavity. 



-The enclosed tip of the axis ultimately becomes the ovule (Figs. 94, 95). 



The primordia of the stamens rapidly elongate, their transverse 



sections becoming oblong with rounded corners. At first they consist 



of homogeneous meristem, but differentiation into dermatogen, periblem, 



FIG. 94. Stages in the development of the carpel ( x 25). 



and plerome with the initials of a central vascular strand is visible 

 when the anther is about -15 mm. in length. 



A single sub-epidermal arche- 

 sporial cell is soon marked out 

 in each corner of the anther. 

 Each of these divides by peri- 

 \ \ / \ i clinal walls into an outer primary 

 parietal cell and an inner primary 

 FIG. 95. Successive longitudinal sections of a sporogenous cell. The former 



young carpel from the centre to the outside ,. ., .. ,, 



(x2s). divides radially, and usually 



after two divisions the four cells 



produced form with the adjoining periblem cells the first parietal layer 

 which encircles the sporogenous cell (Fig. 96). Two successive periclinal 

 divisions follow, resulting in the production of three concentric parietal 

 layers, the inner one in contact with the sporogenous cells becoming the 

 tapetum, the next surrounding zone is the " middle " layer, the third, 



