532 



BOTANY 



PART II 



to a single, spirally-coiled, multiciliate spermatozoid. The female prothallium 

 (Fig. 501), just as in Selaginella, also remains enclosed within the macrospore, and 

 is incapable of independent growth. It shows similarly an approach to the 

 Conifers, in that the nucleus first divides into numerous, parietal daughter-nuclei 

 before the gradual formation of the cell walls, which takes place from the apex of 

 the spore to the base. As a result of this process the whole spore becomes filled 

 with a prothallium, at the apex of which the archegonia are developed. The 

 embryo (Fig. 502) has no suspensor and thus differs from other Lycopodinae. 



Order 5. Sigillariaceae ( 132 ) 



The Sigillarias, found from the Culm onwards, are most numerous in the 

 Carboniferous period, and persist to the Bunter Sandstone. They were stately 



FIG. 503. 1, Lepidodendron. Recoustruction (after POTONIEJ. ..', L. Ac>iJ<-ntinii. cast of stem 

 surface (after STERNBERG). 3, k, Lepidodendron, leaf-cushions (after POTOME). 5, Piece 

 of cortex (after SEWARD). (From LOTSY, Botan. Siammesgeschichte.) 



trees, with but little-branched, pillar-like stems, which grew in thickness. They 

 had long narrow leaves with a ligule, which when they fell off left longitudinal 

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



