INTRODUCTION. 5 



true nature of ferns and allied plants, we shall make the 

 attempt. 



If we examine the backs of a number of fern-leaves (fronds) 

 we shall find that some of them are definitely ornamented with 

 raised dots or lines of a reddish-brown or blackish tint, accord- 

 ing to species. These are heaps of minute capsules (sporangia), 

 each filled with microscopic bodies called spores. Each heap 

 is known as a sorus (plural sort), and is at first covered in most 

 species with a pellicle, which is an outgrowth from the cuticle of 

 the frond, and known as the indusium. The indusium varies 

 greatly in form, but is constant in all the individual plants of 

 the same species, and its characters are utilized in the classifi- 

 cation of the ferns. In the Bladder-ferns, for example, it is 

 inflated, and attached by its broad base. In the Filmy-ferns 

 it forms a capsule split into two valves ; whilst in the Killarney- 

 fern the cup is undivided. The Shield-ferns have a circular 

 indusium attached by the centre of its underside, and the 

 Buckler-ferns have the attachment in a notch in the margin. 

 In the Bracken and the Parsley -fern it is an extension of the 

 turned-down margin of the frond divisions. 



On detaching a single sporange from the sorus it will be seen 

 to be a somewhat globular pouch, with a slender stalk, girdled 

 by a series of specially thickened cells (the annutus, or ring), 

 the thinner portions of which contract by exposure to dry air. 

 They thus exert a strong pulling force upon the walls of the 

 sporange, which ultimately give way and the annulus coils in 

 the opposite direction, the contained spores being scattered by 

 the rupture. The figure (Plate 4) of a sporange of the Male- 

 fern, greatly enlarged, will make the general appearance and 

 structure plain. 



The spores contained in a sporange are, throughout the 



