512 



BOTANY OF THE LIVING PLANT 



contributed largely to the organic remains preserved as Coal. 

 Isoetes appears as the nearest living ally of these fossil plants. 



The Lycopodiales are divided into two series, the Eligulatae, 

 in which a single sporangium is borne in or near to the axil of each 



leaf of the fertile cone, but 

 without any ligule. Here 

 the sporangia and spores 

 are all alike, the plants 

 being homosporous. The 

 Eligulatae include the gen- 

 era Lycopodium and Phyl- 

 loglossum. But Selaginella 

 and Isoetes are included in 

 the Ligulatae, in which 

 the sporangium is accom- 

 panied by a minute scale 

 or ligule borne on the upper 

 surface of each leaf : it 

 is inserted on the distal 

 side of the sporangium 

 (Figs. 407-409). Here the 

 sporangia are of two types, 

 producing respectively male 

 microspores and female 

 megaspores (heterosporous). 

 Most of the fossil Lycopods 

 belong to the Ligulatae. 



Having chosen Dryop- 

 teris and Pteridium as the 

 chief examples of homo- 

 sporous Ferns, — a condi- 

 tion which is shared by 

 Lycopodium among the 

 Club Mosses, — Selaginella 

 will be taken for special 

 treatment as a type of these, while it also illustrates the hetero- 

 sporous state. 



Selaginella. 



A primitive type of Selaginella had an upright radial axis, with 

 leaves of equal size all round it ; and this is the case in 5. spinulosa. 



LYCOPOD/UM, 

 S E LA CO. L. 



J 



Fig. 404 a. 



Whole plant of Lycopodium, Selago, showing ascending 

 and upright habit, as developed when growing protected 

 by Heather. The equal dichotomy and the alternating 

 sterile and fertile zones are seen, and the forking of the 

 roots. Distally bulbils are borne. Reduced. 



