THE REPRODUCTIVE STRUCTURES 



93 



t closely applied to the ''nucellus"; the integument, with 

 parts of the ovule below it, becomes differentiated into 

 three characteristic layers, the outer and inner fleshy, 

 with a stony layer between; the outer fleshy layer 

 finally decays and disappears, while the inner gives up 



Fig. 38. — Sclaginella: longitudinal section of a portion of the cone, 

 showing a microsporangium with microspores at the left and a mega- 

 sporangium with three of its four megaspores at the right; the female 

 gametophyte is shown within the spore. Greatly magnified. 



its nutritive substances to the prothallium — or female 

 gametophyte — growing within, until the fleshy layer 

 becomes reduced to a thin, dry membrane; the stony 

 layer becomes as hard as a hickory nut. 



The ovule is supplied with an extensive vascular 

 system. Two vascular strands from the sporophyll 



