SPERMATOPHYTES 
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 
pollininm. 
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 (s) ; the tapetum has 
broken down (dotted line), and several middle layers are evident. After COULTER. 
