x 9«] LANTIS—ABUTILON THEOPHRASTI 



333 



or less elongated (fig. 5) . 



more 



mother cell is a much 



reduction division follows very closely after the first, no walls 



(figs. 8 



formed 



and 9), a condition characteristic of the dicotyledons. The 



being observed. 



arrangement 



Special study was not made of the composition 

 of the developing microspores, but evidently it is sir 

 microspore walls of Althaea (6), Malm (5), and Ip 

 Since the tapetum reached its highest development 

 formation of the tetrad, the mother cells do not becc 



remain 



While 



formed, the tapetum 

 isappear until the dc 



mature. 



In this respect Abutilon resembles Oenothera (17), Gaura Lind- 

 heimeri (14), etc. 



The mature pollen grain is spherical, has both intine and exine 

 well developed, and is covered with spines (fig. 12). Only two 

 nuclei, the tube nucleus and the generative nucleus, were found in 



the mahirv* 7™!!^ ~..„;~ 



Summary 



Abutilon Theophrasti shows the single row of archesporial cells 

 that has been reported for the other two investigated species of 

 Malvaceae, and in the formation of primary parietal and primary 

 sporogenous layers there is also great similarity. 



In Abutilon, however, each primary sporogenous cell produces 

 four mother cells, while in the other Malvaceae studied only one 

 is formed. 



mother 



ree 



layers, the inner being a well developed tapetum, are fully formed, 

 after which the characteristic heterotypic and homotypic divisions 

 take place rapidly. 



This period oi tetrad formation is marked by a multiplication 

 of nuclei in the tanetal cells. 



