CRYPTOGAMS 467 



ness. They had long narrow leaves, which when they fell off left longitudinal 

 rows of hexagonal leaf-scars on the surface of the stem. Long-stalked, cone-like 

 flowers were borne on the stem ; only one kind of spore was contained in the 

 sporangia. 



The Lepidodendreae extend from the Lower Devonian to the Rothliegende, but 

 are also best developed in the Carboniferous period. They were tree-like plants 

 with dichotomously branched stems which grew in thickness. The leaves, which 

 attained a length of 15 cm., were spirally arranged and seated on rhombic leaf- 

 cushions. The cone-like flowers (Lepidostrobus) were borne on the ends of branches 

 or sprang from the stem itself; each sporophyll bore a single sporangium, which 

 contained either inacrospores or microspores. 



Smaller Lycopodiaceae, the predecessors of the existing species of Lycopodium, 

 were already present in the Carboniferous flora, while Isoetes is only known with 

 certainty from the lower Cretaceous strata. 



4. The small class of the Sphenophyllinae, which existed from the Devonian 

 to the Permian and then died out, possesses special morphological interest since it 

 occupies an intermediate position between Lycopodinae and Equisetinae. Possibly 

 it is the least altered from the common ancestral form of these three groups. This 

 especially holds for the most ancient type Cheirostrobus, which occurs in the Lower 

 Carboniferous rocks. The cones of this genus had a very complicated structure, 

 reminding one of the calamarian cone, while the anatomy exhibits an approxima- 

 tion to the type of Lepidodendron. 



The species of Sphenophyllum were plants with elongated stems, bearing 

 superposed whorls of obcuneate or more or less dichotomously divided leaves. 

 The cones were large and terminal, resembling those of Equisetum ; each sporo- 

 phyll bore two or three homosporous sporangia. These plants have been regarded 

 as aquatic, but the structure of the elongated thin stem, with a triangular mass of 

 primary xylem and subsequent secondary thickening, rather suggests that they 

 were climbing plants which grew on land. 



