4QO 
STRUCTURE AND LIFE HISTORIES 
be considered again later on (page 608). In treating of 
the dicotyledons first, however, we have tacitly assumed 
FIG. 374. Cat-tails. Typha angnstifolia at left; Typha latifolia at right. 
Staminate flowers above; pistillate flowers below. 
that they are the older forms, from which the mono- 
cotyledons have been derived. 
