CYCADALES 



13 



nutrition to functioning mother cells by those which are adja- 

 cent, whether they be morphologically wall cells, sporogenous 

 cells, or even other mother cells, in Cycads is participated in 

 also by some of the mother cells, especially those next to the 

 distinctly organized tapetal layer. The functional mother 

 cells become isolated, and with their complete organization the 

 history of the sporophyte ends, the mother cells entering upon 

 that more or less prolonged resting period preparatory to the 

 reduction division and the beginning of the gametophyte. 



The sporangia dehisce by means of a slit which extends 

 from the base along the side away from the sporophyll and ends 

 in a peculiar group of cells at the apex, whose morphological sig- 



FiG. 10. — Stangeria paradoxa, showing development of miorosporangium ; A, section 

 showing two of the four cells forming the archesporial plate ; B, each cell of the 

 plate has divided into an inner primary sporogenous cell (shaded) and an outer pri- 

 mary wallcell ; C, a more advanced stage ; D, astill more advanced stage, showing 

 the tapetum (shaded) and the sporogenous cells (s) ; E, a mature sporangium con- 

 taining microspores, showing the tapetum (t) and the crushed cells of the wall (w) : 

 A-D, X 266 : JS, a 66.— After Lang. 



nificance is in question. The arrangement of thin and thick 

 walled regions in the sporangium wall, and the mechanism of 

 dehiscence, are said to be essentially as found in Angiopteris. 



