THE PTERIDOPHYTA : FILICALES, THE FERNS 481 



Bower has arranged the Ferns in three biological groups, on the basis of 

 the order in which the sporangia develop. He distinguishes three types : — • 



1. Simp/ices. All sporangia in a sorus develop simultaneously. This 



type is more characteristic of Palaeozoic Ferns than of living genera, 

 but it is shown by the Eusporangiatae and by the Osmundaceae 

 and one or two related families. 



2. Gradatae. Sporangia develop in succession from the apex to the base 



of the elongated sorus. Examples : Hymenophyllaceae, Salviniaceae. 



3. Mixtae. Sporangia develop in the sorus without any fixed order. 



Example : Polypodiaceae. 



It must be understood that this is simply a biological grouping and it is 

 not to be taken as offering an alternative classification, for some families may 

 have genera in more than one group. 



In similar fashion Bower has distinguished two series of Ferns which 

 differ in the position of their sporangia on the leaf. These are the Marginales, 

 in which the sporangia are attached at the leaf margin, e.g., Hymenophyllum 

 and Pteridiiim ; and the Siiperficiales, in which the sporangia are on the 

 lower leaf surface, e.g., Marattia. 



We have chosen to begin our description of the Filicales with the type 

 Dryopteris filix-mas, the Male Fern, in order that the junior student may 

 familiarize himself with the characteristics of this standard type before 

 passing on to those other types which are usually the subjects of more 

 advanced study. 



Leptosporangiatae : Polypodiaceae 



The Polypodiaceae are characterized by the annulus of the sporangium, 

 which is vertical, that is, it lies in the same plane as the sporangial stalk. It is 

 incomplete and does not surround the whole sporangium, which dehisces 

 transversely. The family is very large and widely distributed and its members 

 are mostly herbaceous with erect root stocks or creeping rhizomes. 



Dryopteris filix-mas (The Male Fern) 



The Male Fern occurs commonly in woods and hedgerows (Fig. 469). 

 It possesses a short, blunt, unbranched stem, which grows obliquely upwards 

 through the soil and appears but little above the surface. It increases in 

 diameter with age, so that the top is broader than the lower end, like a carrot. 

 It varies considerably in size, but is seldom more than a foot in length, and 

 appears to be about 4 or 5 in. in diameter, though in reality it is considerably 

 narrower, since the stem is completely covered by the persistent bases of the 

 old leaves, on which adventitious buds sometimes develop and may produce 

 an appearance of branching. 



Compared with some of the Tree Ferns which are found in the tropics 

 and in New Zealand the stem of the Male Fern is insignificant, for the 

 Tree Ferns may reach a height of 60 ft., with a trunk as much as 2 ft. in 

 diameter (Fig. 470). 



