THE MICROSPORANGIUM 



37 



ings on the inner surface of the tapetum (Fig. 30) and later on the 

 inner surface of the middle layers or the endothecium. They give 

 the same staining reactions as the exine of the pollen grains and prob- 

 ably contribute to the development of the latter. This seems to be 

 supported by Gorczynski's (1934) observations on Cardamine, ac- 

 cording to which the exine first begins to develop on that side of the 

 pollen grains which lies towards the tapetum. 



Fig. 30. Tapetal cells, showing cutinization of inner walls. A, Magnolia youlan, 

 tapetal cell, showing prominent thickenings on inner surface. B, the thickenings 

 as seen in surface view. C, Lilium tigrinum, thickenings on inner walls of tapetal 

 cells. D, same in surface view. E, more highly magnified than D. (After Kos- 

 math, 1927.) 



Sporogenous Tissue. The primary sporogenous cells give rise 

 to the microspore mother cells. In some plants the sporogenous 

 cells undergo several divisions, in others only a few divisions, and 

 rarely there are no divisions at all, so that the primary sporogenous 

 cells function directly as the microspore mother cells. Alangium, 

 Sansevieria, Knautia, and some members of the Malvaceae and 

 Cucurbitaceae are examples of the third kind, showing a single row 

 of microspore mother cells in each anther lobe. 



