228 MOSSES AND FERNS chap, viii 



upon the lower surface, necessitates a bending upward of the 

 growing point of the young sporophyte, which is not the case 

 in B. Virginianum, where the archegonium is above, and the 

 sporophyte grows up vertically from the beginning. 



Mettenius' account of the development of the embryo in 

 O. pedunculosum is somewhat more 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 (Fig. io8, E). The upper part, 

 i.e. that next the archegonium neck, grows up at once into the 

 cotyledon, v^'hile the opposite part gives rise to the first root. 

 These grow respectively 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 

 here 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, especi- 

 ally where the prothallium forks. 



Ophioglossuni {Ophiodermd) pendulum^ an epiphyte common 

 in the Eastern tropics, may be taken as a type of the simplest 

 of the Ophioglossaces. 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 sporiferous 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. 

 114, C) and no free ends. Sections of the spike cut parallel 

 to its broad diameter show a somewhat similar arrangement of 

 the vascular bundles, but here there are free branches extending 

 between the sporangia. The relations of the bundles of the 

 fertile and sterile parts of the leaf are best followed in the 



