FILICINEAE. HOMOSPOROUS FILICINEAE. 227 



Taxonomic summary of the homosporous Ferns. The main divisions are as 

 follows : 



1. HYMENOPHYLLEAE. The sporangia have an oblique or transverse complete 

 annulus and open therefore by a longitudinal fissure; they are formed on a pro- 

 longation of the fertile vein, the columella or placenta, which projects beyond the 

 margin of the leaf and is surrounded by a cup-shaped indusium. The mesophyll of 

 the leaf is usually formed of a single layer of cells, and in that case is necessarily 

 without stomata ; stomata are found on the leaf of Loxosomd, which has more than one 

 layer. The stem is often creeping and usually very slender and furnished with an axile 

 vascular bundle. True roots are not found in all the species ; where they are wanting 

 the stem is itself clothed with root-hairs ; a large number of species of Trichomanes 

 were considered by Mettenius to be without roots, and in these cases the ramifications 

 of the stem assume a deceptive appearance of roots. The axes grow more rapidly than 

 the leaves develope, and it is not uncommon for several internodes to have fully com- 

 pleted their growth while their leaves are still quite small ; these apparently, or 

 perhaps really, leafless shoots often branch repeatedly. The formation of the tissue 

 also has many peculiarities, on which Mettenius should be consulted (Hymeno- 

 phyllaceae, /. <:.). The fertile extremity (columella) of the vein, which projects beyond 

 the margin of the leaf, elongates by intercalary growth, and new sporangia are 

 accordingly produced in basipetal succession ; they are arranged on the columella in 

 a spiral line, and are sessile and biconvex, being attached to the columella by one of 

 the convex faces. The annulus which forms a cushion-like protuberance between the two 

 convexities is usually oblique and divides the circumference into two unequal portions ; 

 in Loxosoma the sporangia are pear-shaped and distinctly stalked. Paraphyses occur 

 in some species of Hymenophyllum only. 



2. CYATHEACEAE. The sporangia have a complete, oblique excentric annulus and 

 a short stalk, and are placed on a placenta which is often greatly developed ; they 

 form a sorus which is usually closely packed, and is either naked or surrounded by 

 a cup-shaped indusium which sometimes forms a closed capsule. The Tree-ferns are 

 included in the genera Cibotium^ Balantium, Alsophila, Hemitelia, and Cyathea ; they 

 have tall erect unbranched stems often thickly clothed with roots, which bear on their 

 tops a rosette of large usually compoundly pinnate leaves. 



3. POLYPODIACEAE. The sporangia are very numerous on the under side of usually 

 unaltered leaves with a vertical incomplete annulus, and they dehisce transversely. 

 The very numerous species have been arranged by Mettenius in the following sub- 

 divisions : 



a. Acrosticheae. The sorus covers the mesophyll and veins of the under surface or 

 of both surfaces of the leaf, or is placed on a thickened placenta running along the 

 vein : there is no indusium (Acrostichum> Polybotryd], 



b. Polypodieae. The sorus is attached along the course of the veins, or of special 

 anastomoses of the veins, or on the back or on the thickened extremity of a vein ; it is 

 naked or rarely has a lateral indusium (Polypodium^ Adiantum^ Pteris). 



c. Asplenieae. Sorus unilateral on the course of the veins, and almost always 

 covered with a lateral indusium, seldom without an indusium, or the apex of the sorus 

 arches over the back of the vein and is covered by an indusium that springs from it, or 

 it occupies special anastomoses of the veins, and is unilateral and covered by an 

 indusium which is free on the side of the vein ; the leaf-stalk is not articulated 

 (Blechnum, Asplenium, Scolopendriuni). 



d. Aspidieae. The sorus is dorsal with an indusium, rarely terminal and without an 

 indusium (Aspidium, Phegopteris). 



e. Davallieae. The sorus is terminal or where a vein forks with an indusium, or on 



1 One species only of this genus is known from New Zealand, and by some botanists is made 

 the type of a distinct family. 



Q 2 



