VEGETATIVE REPRODUCTION. 217 



branches ; or they are produced in spore cases, which break 

 or are broken to set free the spores. The parts producing 

 the spores are usually numerous and are closely associated. 



In the fernworts and seed plants the spore cases are usually 

 formed on specialized leaves. When such leaves are clus- 

 tered on a short stem, and especially when they are accom- 

 panied by colored accessory leaves, they form a flower. The 

 accessory leaves form the perianth (calyx and corolla) and 

 the spore-bearing leaves are the essential organs (stamens 

 and pistils). The stem from which they grow, the torus, is 

 often enlarged when the leaves are numerous. 



Brood buds are usually larger and more complex than 

 spores. In the lower plants they show no distinct members. 

 In the fernworts and seed plants they^ often have rudiments 

 of leaves and stems. Similar, but more developed parts, are 

 separated by some plants to form new individuals. Propa- 

 gation by cuttings, grafting, and budding is merely an imita- 

 tion of natural methods. 



