VII PTERIDOPHYTA—FILICINEJE—OPHIOGLOSSACEJE 245 



According to Mettenius, the cotyledon in Ophioglossum 

 pedunculosum develops much earlier than is the case in 

 Botrychiuni. It appears above the ground while the primary 

 root is still but little developed. (Fig. 125, B.) 



In Botrychium lunaria, according to Hofmeister, the first 

 three leaves are rudimentary and the first green leaf does not 

 appear above ground until the second year. 



Mettenius' account of the development of the embryo in 

 O. pedunculosum is less complete. The earliest stage seen by 

 him was already multicellular, and the young embryo had the 

 form of an oval cell mass in which the primary divisions were 

 not recognisable. The upper part, i. e., that next the arche- 

 gonium. neck, grows up at once into the cotyledon, while the 

 opposite part gives rise to the first root. These grow respect- 

 ively upward and downward) and break through the overlying 

 prothallial cells. Later, at a point between the two, the stem 

 apex is developed. The first leaf becomes green, and develops 

 a lamina similar to that of the later-formed ones. Usually but 

 one embryo is developed from the prothallium, but occasionally 

 two are formed, especially where the prothallium forks. 



The Adult Sporophyte 



Ophioglossum (Ophioderma) pendulum, an epiphyte com- 

 mon in the Eastern tropics, may be taken as a type of the sim- 

 plest of the Ophioglossaceae. Its short creeping stem grows 

 upon the trunks of trees, especially tree-ferns, from which the 

 long flaccid leaves hang down. The lamina of the leaf merges 

 insensibly into the stout petiole whose fleshy base forms a sheath 

 about the next younger leaf. Corresponding to each leaf is a 

 thick unbranched root, which penetrates into the crevices of 

 the bark and holds the plant secure. These roots are smooth, 

 and show no trace of rhizoids. The petiole is continued up into 

 the lamina as a very broad and thick midrib, which in the spo- 

 riferous leaves (sporophylls) is continued into the peculiar 

 elongated spike which bears the sporangia. 



The petiole if cut across shows a number of vascular bundles 

 arranged in a single row, nearly concentric with the periphery 

 of the section. As these enter the lamina they anastomose and 

 form a network with elongated meshes (Fig. 133, C) and no 

 free ends. Sections of the spike cut parallel to its broad 



