CHAPTER XVIII, 



ACROSTICHUM, Linnmus. 

 (Ac-ros'-tich-um.) 



HIS very extensive genus, which, in Hooker and Baker's 

 " Synopsis Filicum," is given as genus 60, and which forms by 

 far the greatest portion of the Acrostichece (Ac-ros-tich / -e-£e), 

 is composed almost exclusively of tropical Ferns, and comprises 

 various groups with a wide range of venation and cutting. 



For diversity of foliage, as also for variation in habit, few other genera 

 can compare with Acrostichum, as it embraces plants of the smallest dimen- 

 sions, and others of quite gigantic size, as well as plants with simple 

 (without distinct ramifications) or entire fronds, and others with fronds 

 pinnatifid (divided half-way to the midrib in segments in a feathery manner), 

 pinnate (divided to the midrib in a feathery manner), or even bipinnate 

 (doubly pinnate). The distinguishing characters of Acrostichum proper reside 

 in the nature and in the disposition of the sori (clusters of spore-cases), 

 which are spread over the whole under- surface of the fertile fronds, or of 

 their upper pinnse (leaflets) — or, occasionally, over both surfaces — and are 

 not confined to the veins only. 



The following are the various groups included in this genus : 



Aconiopteris (Ac-on-i-op'-ter-is), Presl. — Fronds simple ; veins anas- 

 tomosing (intermixed), united only near the margin. 



Chuysodium (Chry-so'-di-um), Fee. — Plants with fronds dimorphous (of 

 two different forms), or sometimes with the upper pinnse like the others, 



