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 

 ' ^>\ m eac h corner of the anther. 

 ([ | Each of these divides by peri- 

 clinal walls into an outer primary 

 parietal cell and an innerprimary 

 sporogenous cell. The former 

 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, 



FIG. 95. Successive longitudinal sections of a 

 young carpel from the centre to the outside 

 (X25). 



