SELAGINELLA SPOROPHYTE 271 



bud. In the lower part of the sections a mature 

 sporangium may be found in the axil of each leaf. 

 The sporangium may have lost its spores partially or 

 entirely during the preparation of the sections. It will 

 consist of 



a. A short massive stalk. 



5. A wall inclosing the central cavity : the wall 

 will be found, under a high power to consist of three 

 layers of cells 



i. The outer consisting of thick-walled cells, more 

 or less elongated radially. 



ii. A layer of small, compressed cells. 



iii. A layer of thin-walled cells, elongated radially : 

 this is the tapetum, which is here persistent until the 

 spores are ripe. 



Surrounded by the wall will be found 



c. Spores of two sorts, contained in different 

 sporangia 



i. Microspores of relatively small size : these will 

 be found in large numbers in certain sporangia, which 

 will accordingly be recognized as microsporangia. 

 When ripe they may be still seen to cohere in groups 

 of four : each spore is a single cell with a brown wall. 



ii. Macrospores of relatively large size : four only 

 of these will be found inclosed in a single sporangium, 

 which is accordingly termed a macrosporangium. 

 Each spore consists of a thick wall, with numerous ex- 

 ternal projections, surrounding a large cavity filled with 

 protoplasm, &c. 



The development of the sporangium may be traced in longi- 

 tudinal sections of sporangium-forming cones which have been 

 hardened in alcohol, or in picric acid and then in alcohol : mount 



