150 



PLANT STRUCTURES 



tendency to restrict the sporogenous tissue and increase the 

 sterile tissue. It will be observed that with the introduc- 

 tion of the leafy sporophyte among the Pteridophytes the 

 sporangia appear much later in its development, sometimes 

 not appearing for several years, as though they are of 



<~cs. 







-'.CD 

 .^ 



FIG. 131. A series showing the dehiscence of a fern sporangium, the rupture of the 

 wall, the straightening and bending back of the annulus, and the recoil. After 

 ATKINSON. 



secondary importance as compared with chlorophyll work ; 

 and that the sporogenous tissue is far more restricted, the 

 sporangia forming a very small part of the bulk of the 

 sporophyte body. 



