40 



STRUCTURAL BOTANY 



gradual strengthening of the growing -point. In this 

 respect, though in no other, Ferns resemble the Mono- 

 cotyledons (see Part I. p. 173). 



The leaves, often called Fronds, are of very large size, 



one to three feet 

 long, and much 



subdivided (see 

 Figs. 17 and 18). 

 This is the first 

 example of a com- 

 pound leaf we have 

 had. A compound 

 leaf is one in which 

 thelamina or blade 

 is completely sub- 

 divided, so that 

 its several parts, 

 called leaflets, re- 

 semble distinct 

 leaves. The leaves 

 of the Male Fern 

 are pinnate, that 

 is, the main stalk 

 or rachis, bears 

 two rows of leaf- 

 lets, oxpinnce, one 

 row on each side 

 (see Fig. 18). The pinnae are often subdivided them- 

 selves in the same way, and then the whole leaf is 

 said to be li-pinnate. In the specimen figured, the 

 pinnse are deeply lobecl, but not completely subdivided. 

 Each lobe, like that shown singly in Fig 18, B, may 

 be called a segment. The segment is traversed by 



- 



KJ^^M<2^ il ^nfi'i* > ' 





Fio. 1 8. A, leaf of Hale Fern (much reduced). 

 B, part of a fertile pinna seen from below ; 

 a, rachis ; s, sorus. Magnified. (After 

 Luerssen.) 



