528 



A TEXTBOOK OF THEORETICAL BOTANY 



part in the formation of the sporangium, especially in that of the stalk. It 

 is therefore not strictly Leptosporangiate. The initial cell is usually 

 pyramidal, but cubical cells are also to be found, and these latter are plainly 

 similar to the archesporial cells of that shape which are to be found in the 

 Eusporangiatae (Fig. 526). The initial cell divides into two horizontally, 

 cutting off a primary wall cell above and an archesporial cell below. The 

 wall cell divides anticlinally to form a single layer of wall cells. The arche- 

 sporial cell also divides parallel to all its faces and cuts off a second series of 

 peripheral cells, which form an inner layer of the wall. The remaining 



*^~'K ARCHESPORIUM 



MA./' X 



TAPETUM 



SPORE 

 MOTHER 

 CELLS 



STOMIUM 



CAP OF 

 THICKENED 

 CELLS 



Fig. s^b.—Osihunda re^alis. Development of sporangium. A to C, Ongm from a group 

 of cells, showing cubical and pyramidal archesporial cells. D and E, Development of 

 archesporium. F, Spore mother cells. G, Dehiscent sporangium showmg cap of 

 thickened cells. (A to D after Boiver, E to G after Smith.) 



central cells divide repeatedly and produce a mass of sporogenous cells, 

 the outer layer of which becomes the tapetum, which later breaks down into 

 a Plasmodium, and penetrates between the developing spores. The cells of 

 the floor of the sporangium may also contribute to build up this tapetum, a 

 procedure which again recalls the Eusporangiatae. The sporangia are normally 

 single, but synangia sometimes occur. The fertile sporogenous cells function 

 as spore mother cells and undergo meiosis to produce spores. The number 

 formed is always large, but appears to be variable, counts between 256 and 

 512 being recorded. 



