PTERIDOPHYTA 



143 



peculiarity has been recently detected in one of the 

 living species of Equisetum. 



Associated with some of the fossil forms there are 

 found cones, which evidently 

 belong with them, and resemble 

 those of the existing Equisetum. 

 In a few instances they have 

 been preserved so perfectly that 

 the inner structure can be accu- 

 rately made out, and it is evi- 

 dent that the tissues and spo- 

 rangia of these plants closely 

 resembled those of Equisetum, 

 although most of them exhibit 

 a degree of specialization not 

 found in any of their living 

 relatives. The Equisetinese rap- 

 idly diminish in importance in 

 the later geological epochs, until, 

 as we have seen, but a single 

 genus has survived to the pres- 

 ent time, and this is one of the 

 less specialized types. 



FIG. 37 (Lycopodine?e). A, 

 part of a plant of a club- 

 moss (Lycopodium clava- 

 tum) with two sporangia! 

 spikes, sp ; B, a sporophyll 



LYCOPODINE^E 



from the spike of L. den- 

 droideum, bearing a single 

 large sporangium, sp ; C, 

 cross-section of the stem ; 

 vb, the central vascular 

 cylinder. 



The third class of Pterido- 



phytes, the Club-mosses, is intermediate in point of num- 

 bers between the two already considered. There are 

 three well-marked orders, of which the first, Lycopodi- 

 acese, includes the common club-mosses belonging to 

 the genus Lycopodium. The second order, Selaginel- 



