EXPLANATION OF TEKMS 



FIG. 4 



A frond is once-pinnate when the incisions extend 

 to the mid vein (Fig. 3). Under these conditions 



the midvein is called 

 the rachis (a), and the 

 divisions are called the 

 pinnce (b). 



A frond is twice-pin- 

 nate when the pinnse 

 are cut into divisions 

 which extend to their 

 midveins (Fig. 4). 

 These divisions of the 

 pinnae are called pin- 

 nules (a). 



A frond that is only once-pinnate may seem at 

 fivst glance twice-pinnate, as its pinnas may be so 

 deeply lobed or pinnatifid as to require 

 a close examination to convince us that 

 the lobes come short of the midvein 

 of the pinnae. In a popular hand-book 

 it is not thought necessary to explain 

 further modifications. 



The veins of a fern are free when, FlG - 5 

 branching from the midvein, they do not unite with 

 other veins (Fig. 5). 



Ferns produce spores (Fig. 6) instead of 

 seeds. These spores are collected in spore- 

 cases or sporangia (Fig. 7). Usually the 

 sporangia are clustered in dots or lines on 

 the back of a frond or along its margins. 

 These patches of sporangia are called sort or fruit- 



FIG. 6 



