PTERIDOPHYTA-^FILICIN^ 139 



is soon segmented into epibasal and hypobasal parts by the 

 formation of a basal wall parallel to the axis of the archegonium. 

 Each gives rise b^' further divisions to four octants. In 

 further development the epibasal octants give origin to the stem 

 and first leaf, or cotyledon, of the young sporophyte ; the hypo- 

 basal ones form the primary root and a special organ, called the 

 foot, which attaches the young fern to the prothallium, from 

 which it draws a supply' of nutrient material. The foot becomes 

 a somewhat bulky structure and occuj)ies the space formed by 

 the venter of the archegonium {fig. 880). 



The primary root soon disappears ; the cotyledon also lasts 

 but a short time, and is succeeded by the foliage leaves, arising 

 from the stem. The foot also disappears as soon as the young 

 fern has become capable of absorbing its nutriment from its 

 environment independently of the gametophyte. 



The prothallium seldom lives longer than is necessary to 

 produce a single sporophj^te. The sporophyte, on the contrary, 

 may produce spores for many years, each being able to give rise 

 to a gametophyte. Sometimes the gametophyte lives longer, in 

 some cases for more than a year. 



The vegetative reproduction of ferns occurs in both genera- 

 tions. The gametoph^'te may give rise to branches or to gemmae, 

 either of which can develop into prothallia. The sporophj-ll maj- 

 produce adventitious buds, generally on the petioles of its leaves 

 where the^' are below the soil. 



Both apospory and apogamy may occur in this group. 



Section 2. — Isosporous Eusporangiate Ferns. 



In this section are comprised two orders of Ferns, the 

 Ophioglossaceae and the Marattiaceae, which have much in 

 common with the previous group, but differ in that their spo- 

 rangia are derived each from a group of superficial cells instead 

 of from a single one. 



OPHIOGLOSSACEiE. 



The affinities of the Ophioglossaceae have lately been much 

 discussed, and many doubts have been suggested as to their 

 being properly included among the ferns, certain points in their 

 structure suggesting an affinity with the Lycopodinae. For the 

 present, however, it will be well to give them their old position. 



The sporophyte is generally a short erect rhizome bearing a 

 few leaves which are not circinate in vernation. Generally 



