SPERMATOPHYTES 



135 



grains (microspores). It is these sacs, usually consisting of 

 two fused microsporangia, that are called pollen-sacs in 



FIG. 105. Cross-section of a very young anther of a lily, showing the four developing 



sporangia. 



Angiosperms. A pollen-sac opens to discharge the pollen, 

 usually by splitting down the line where the two microspo- 



FIG. 106. Cross-section of a mature anther of a lily (much larger than that shown in 

 Fig. 105), showing the two chambers formed by the four sporangia, and also the 

 region of opening for each chamber (s). 



