SPERMATOPHYTES 



259 



Fig. 579. — Transverse section of a young anther of lily, showing the four sporangia 

 well advanced. — After Coulter. 



spores of a sporangium cling together in one mass, called the 

 pollinium. 



As the four sporangia of an anther increase in size (fig. 579), the sterile 

 tissue separating the two sporangia on each side of the anther breaks 



Fig. 580. — Transverse section of a mature anther of lily, showing the sporangial 

 cavities fused to form two pollen sacs (which are full of pollen grains); the endothecium 

 conspicuous (just beneath a more or less fragmentary epidermis), and also the re- 

 markable cells formed by the epidermis at the line of dehiscence (i) ; the tapetum has 

 broken down (dotted line), and several middle layers are evident. — After Coulter. 



