512 



INTRODUCTION TO CRYPTOGAJIIC BOTANY. 



when it is considered that the archegonium here produces 

 something Hke an embryo, 



573. In no branch of Cryptogams, not even in mosses, are 

 the principles on which the systematic arrangement is formed 

 more vague and uncertain than in Ferns. One founds his divi- 

 sions on the indusium (Fig. 113, b), another on the ring (Fig. 

 113, cl), another on the venation, and another on the nature of 

 the rhizoma. Though all these points are valuable, none is of 

 such predominant importance as to exclude the others. If the 

 obliquity of the ring were strictly attended to, the closest allies 

 would he separated. The near affinity of Polypodium and 



Fig. 114. 



a. Sporangium of Aneinda 

 aurita^ Sw. From Hook. Cent., 

 tab. 3. 



b. Ditto of Osmunda regalis. 



Fig. 115. 



a. Sporangium of Gleichenia 

 Cunninghamn, Hew. 



b. Ditto of Hymenophylhim 

 indcherrimnm, Col. 



Both received from Dr. Hooker. 



Polystichurfi speaks strongly against too strict attention to the 

 indusium. One of the strongest instances of its uncertainty is 

 afforded by Polypodium rugulosum and HyiJolepis tenui- 

 folia, species which have an extremely wide distribution, and 

 which are, probably, one and the same Fern. But allowing 

 the two to be distinct, there is great variation in the former, 

 as regards the position of the sori. In some specimens they 

 recede from the margin, in some they are close up to it, as if 

 prepared for an indusium. And then touching H. tenuifolia 

 I have specimens given to me by Dr. Hooker, from six 

 different localities, in one of which the involucre is incomplete; 

 in another herbaceous ; in another cartilaginous ; in a fourth 

 herbaceous, with a membranous edge ; in a fifth membranous ; 

 and in a sixth indifferently membranous and herbaceous. It 

 is highly injudicious, therefore, to lay too much stress upon 



