DIVISION III. 

 PTERIDOPHYTA. 



CHAPTER XX. 



(A) LYCOPODIALES. 



WE now leave the Seed-Bearing Plants. The Seed which characterises 

 them includes parts which belong to three generations. The Seed- 

 Coat is part of the parent Sporophyte. The Endosperm, whether 

 temporary or persistent to ripeness, represents the Gametophyte 

 generation. The Germ is the new generation derived from it. The 

 Seed is thus a composite structure, and being so it cannot have been 

 of primitive origin. Its real nature, and how it was produced in the 

 course of Descent can only be explained by comparison of Plants 

 lower in the scale, belonging to the Division of the Pteridophytes ; 

 for it is from such seedless types that the Seed-Plants have arisen. 



The Pteridophyta include the Club-Mosses (Lycopodiales), the 

 Horse-tails (Equisetales), and the Ferns (Filicales), together with some 

 other less familiar types of Plants, some of which are only known as 

 Fossils. All of these are represented in the Palaeozoic Period. There 

 is thus no doubt of the extreme antiquity of these types, which is 

 shown by- their characters as well as by their history. An important 

 feature which they all share is that the female organ is a flask-shaped 

 body called an archegonium. Such a body has already been seen in 

 Gymnosperms, and it is also found in the Mosses (Bryophyta). In 

 fact the archegonium is the general type of female organ for all the 

 primitive Plants of exposed Land-Surfaces, which may accordingly 

 be styled collectively, the Archegoniatae. For the present purpose 

 of comparison with Seed-Plants a few examples selected from the 

 Pteridophyta will suffice, of which the most important will be the 

 genus Selaginella from the Lycopodiales, and some common Fern 

 from the large series of the Filicales. 



