2 DESCRIPTIVE CATALOGUE 



Group PTERIDOPHYTA. 



Plants in which the alternation of generations finds expres- 

 sion iu distinct, alternating individuals of very different types 

 of organisation. The sporophytic generation is generally large, 

 leafy, and provided with definitely differentiated vascular tissue; 

 the gametophytic generation, on the other hand, is generally 

 small, often minute, and very simply organised, and is without 

 specialised vascular tissue, lleproduction in the sporophyte is 

 by means of simple spores, produced generally on the foliage, 

 which germinate rapidly in moisture to produce the gameto- 

 phyte on which differentiated egg and sperm cells develop. 

 In fossil remains we generally find only the sporophytic 

 generation. 



The organisation of the sporophyte varies enormously, from 

 huge forest trees with massive woody trunks to the delicate 

 plantlets of the filmy ferns. In the Palaeozoic period the 

 Pteridophyta produced cambiums which gave rise to masses of 

 secondary wood: among living forms very few genera have 

 any secondary thickening, and this is always very irregular 

 and small in amount. 



There are two principal lines of development in the Pterido- 

 phyta, the microphyllous and the megaphyllous. The micro- 

 phyllous LycopodinesB have but few representatives in the 

 Mesoxoic rocks, in which the two leading groups arc the 

 Equisetinac and the Filicinre. The former have small, narrow 

 leaves arranged in definite, cyclic whorls on the straight, sym- 

 metrically branching stems, with spores in definite cones, pro- 

 vided with simple peltate sporophylls : the latter have large, 

 often compound leaves, irregularly branched stems, and spores, 

 generally in sori, on the foliage leaves. 



Class FILICIN^l. 



Vegetative habit of the sporophyte very various ; stems aerial 

 or underground, irregularly branched. True roots, principally 

 adventitious, are diarch in the majority of families. Lamime 

 of the foliage leaves simple or exceedingly divided into bi-pinnate 

 large fronds. Sporangia, with or without annulus, sometimes 



