THE FLOWER 



ii' 



immediately beneath the epidermis, developing into the endothecium 

 of the mature anther. 



For a time the sporogenous cells form a single longitudinal row. About 

 the period when the tapetum is formed they divide both radially and 

 longitudinally ; in a median longitudinal section two rows are seen at 

 this stage, a transverse section usually showing six radially arranged 

 cells, all of which on their outer surfaces are in contact with the tapetum ; 

 these are transformed without further division into pollen mother-cells, 



FIG. 96. i, Transverse section of a young anther, showing initial archesporial cells at 

 each corner ; 2, first division of archesporial cell ; 3-6, transverse sections of portions 

 of an anther, showing subsequent divisions ; 7, longitudinal section of 6 ; p, d, sporo- 

 genous cells (x 260). 



which separate as the anther loculi enlarge, becoming free spherical or 

 oval cells about 35 /n in diameter, each with a large central nucleus. 



The free pollen mother-cells, which usually form a single layer lining 

 the enlarged loculus (Fig. 98), undergo two successive divisions, the first 

 being the reduction division, the daughter nuclei receiving in some races 

 of wheats eight short chromosomes. 



The number of chromosomes, however, is not the same for all races of 

 wheat, and variations have been recorded in different cells of the same 

 individual plant. 



