LIFE HISTORY OF A LIVERWORT 



219 



not all mature at the same time, as in the mosses and 

 ferns, but new spores continue to" form in the region of 

 intercalary growth so long as growth continues. As the 

 spores mature the tip of the sporophyte splits open, and 

 the walls spread apart progressively, as spores lower down 

 come to maturity. 



Fig. 165. — Anthoceros. Photomicrograph of a longitudinal section of 

 the sporogonium, and portion of the gametophytic thallus. Note the 

 foot of the sporogonium, and the more darkly stained spores at the center, 

 above. 



200. Distribution of Spores. — In addition to spores, a 

 portion of the tissue of the archesporium develops sterile 

 cells or cell-rows, called elaters (Fig. 166). When these 

 become dry, as the sporogonium splits open from the. tip, 



