SECT. I 



CRYPTOGAMS 



415 



also, essentially with that of the Fern-embryo, except that the first 

 leaves are arranged in a whorl and encircle the apex of the stem. 

 The growth of the embryo is effected by 

 the division of a three-sided apical cell 

 (Figs. 162, 163, pp. 149, 150). 



The outer epidermal walls of the stem are more 

 or less strongly impregnated with silica. In 

 Equisetum hiemale, and to a less degree in Equi- 

 setum arvense, the silieification of the external 

 walls is carried to such an extent that they are 

 used for scouring metal utensils and for polishing 

 wood. 



Equisetum giganteum, growing in South America, 

 is the tallest species of the genus ; its branched 

 haulms, half supported by neighbouring plants, 

 attain a height of over ten metres. 



The extinct Oalamarieae, which form a special 

 class of Pteridopliyta, and resemble most nearly the 

 Equisetinae, attained their, highest development in 

 the Carboniferous period. Their jointed stems, 

 similar to those of the Horse-tails, the so-called Fig. 348.— Equisetum arvense. Male 

 Calainites, attained the dimensions of a tree and prothallium with three anther- 

 bore at the nodes vertieillately - leaved branches. ^^bo ?' ^"^ Ho ™ E1ST ™' 

 These branches, which have also been described as 



special genera, Annularia and Asterophyllites, may in part have belonged to smaller 

 herbaceous forms. It has been determined with certainty that the sporophylls of 

 the cones of some species bore both macro- and microsporangia ; while other species 

 were homosporous. In the primary structure of the stems the Calamites corre- 

 spond essentially with the Equisetinae, but differ from them in possessing secondary 

 growth in thickness, similar to that of Gymnosperms. 



Class III 



Lycopodinae (Club Mosses) 



To the Lycopodinae belong, as their most important and widely 

 distributed genera, Lycopodium, Selaginella, and Isoetes. They are dis- 

 tinguished from the other Pteridophyta, of which they resemble most 

 nearly the eusporangiate Filices, by their general habit and the mode 

 of their sporangial development. 



Unlike the fertile leaves of the Filicinae and Equisetinae, which 

 always bear numerous sporangia, the sporophylls of the Lycopodinae 

 produce the sporangia singly, at the base of the leaves or in their 

 axils. Although in many cases scarcely distinguishable from the sterile 

 leaves, the sporophylls are frequently distinctively shaped, and, like 

 those of Equisetum, aggregated at the ends of the fertile shoots into 



