206 THE EVOLUTION OF PLANTS 



scales together with sterile, protective bracts. In 

 the commonest type of Calamitean fructification, 

 the arrangement is this: a whorl of fertile scales 

 alternates regularly with a whorl of sterile bracts 



Fig. 23. Longitudinal section of part of the cone of a 

 Calamite; (br) bracts; (sp) fertile scales. X 8. (A) Group 

 of four spores, of which three are visible; (B) another group, 

 in which three spores are abortive; (C) megaspore and abor- 

 tive spores from another species. A, B, C X about 100. 

 From drawings by Mrs. D. H. Scott. 



all the way up the cone, and the distances between 

 the whorls are equal, so that the fertile scales come 

 exactly midway between two whorls of sterile 

 bracts and vice versa (fig. 23). Usually the bracts 

 in a whorl are about twice as numerous as the 

 fertile scales. 



