48 EVOLUTION IN THE PAST 



phyllum). More stalwart were the growths of less wide 

 relationships, and represented by existing club-mosses. The 

 latter, possessing an outward appearance to mosses, are in 

 many cases not larger than those plants. Even in tropical 

 regions they are at best but shrubs and bushes. Very different 

 was the condition of their ancestors. As early as the Devonian 

 Period many growths of this type were big, branching trees, 

 towering far above most of the other vegetation (Lepidoden- 

 dron, Bothrodendron). 



Occasionally rivalling them in height other forms with reed- 

 like stems, ringed at intervals with leaves (generally of 

 lanceolate shape), adorned the scenes (Calamodadus, Archceo- 

 calamites}. These growths, known as calamites, attained 

 great importance, whilst the plant world still was young ; but 

 they have long since dwindled, and to-day are represented 

 only by the humble " horsetail " (Equisetum). 



FERNS Ferns were increasing in variety ; and some forms (Astero- 

 chlana) apparently were forerunners of certain tropical 

 species of our own time (Marattiacea}. 



CYCAD-FERNS In addition to ferns and other spore-producing growths, 

 there were several fern-like plants which through frond- 

 modifications had passed or were in process of passing from 

 a spore-bearing to a seed-bearing stage (Alethopteris, Mega- 

 lopteris). As the growths were in a condition of development 

 between ferns and cycads, they are known as cycad-ferns 

 (Cycadofilices). Their appearance in plant-life was a notable 

 event, for it indicated a safer and more economical method 

 of reproduction than had hitherto prevailed. A spore is in an 

 ill-nourished condition when it leaves its parent, and, being 

 without an embryo, it cannot give rise forthwith to a plant 

 resembling the parent-form. Owing to their starved condi- 

 tion, and as the production of an embryo is a roundabout 

 and hazardous process, spores are produced in enormous 

 quantities. In the case of seed-bearers such profusion is 

 unnecessary, as the principle of parental care is much more 

 pronounced. Seeds are fertilised and well-nourished before 

 leaving the parent, and are in a condition to give rise forth- 

 with to growths resembling their parents. Fern-cycads, 

 therefore, testified to a safer and more economical method of 



