38 STRUCTURAL BOTANY 



genera and about forty species are represented. The limits 

 of both genera and species are, however, very indefinite 

 among the majority of Ferns. The Ferns are the only 

 order of Vascular Cryptogams which has successfully held 

 its own down to the present day, while the other groups 

 are represented by comparatively few surviving forms. 



It need hardly be said that among this immense 

 family of plants every possible variety of habit is to be 

 found, while in structure the differences are scarcely less 

 great. In size, we find every gradation, from the Tree 

 Ferns of the tropics and New Zealand, which may reach 

 60 feet in height, down to minute Filmy Ferns hardly 

 larger than Mosses. The main outlines of the life- 

 history are, however, with few exceptions, fairly uniform 

 throughout. 



The particular Fern which we have chosen as a type 

 serves well to illustrate the chief points in the develop- 

 ment and morphology, but we cannot expect any single 

 representative to give a fair conception of the Order as a 

 whole. 



I. EXTERNAL CHARACTERS 



A. VEGETATIVE ORGANS 



The Male Fern, one of the commonest British Ferns, 

 grows abundantly in woods and hedgerows. The short, 

 stout stem grows obliquely upwards, and rises but little 

 above the surface of the ground. It often reaches a 

 length of about eight inches and a diameter of about one 

 inch ; but it appears much thicker than it really is, 

 because it is completely covered with the bases of the 

 old leaves. 



The stem at first has the form of a cone with the 

 thin end downwards ; for it grows thicker for a time 



