X FILICINE.-E LEPTOSFORANGIA T.E 305 



may have an unlimited growth. Such buds may have the 

 form of ordinary branches, or they are of a special form. 

 Buds of the latter class occur, sometimes in great numbers, in 

 certain Hymenophyllacca^, where they are formed upon the 

 margin of the prothallium, to which they are attached by short 

 unicellular pedicels from which they readily become detached. 

 In this way, as well as by the separation of ordinary branches, 

 the prothallia of some species of HyinenopJiylliun form dense 

 mats several inches in diameter, which look' exactly like a 

 delicate Liverwort. A most remarkable case is that of Gyinno- 

 gramme leptopJiylla, examined by Goebel.^ The prothallium 

 multiplies extensively by buds, some of which form tuber-like 

 resting bodies, by which the prothallium becomes perennial. 

 The sporophyte in this species is annual and dies as soon as 

 the spores ripen. The archegonia are borne on special branches 

 of the prothallium, which penetrate into the ground and lose 

 their chlorophyll. Goebel ^ suggests what seems very probable, 

 that the subterranean prothallium of the Ophioglossaceae may 

 be of this nature, and the fact that in Botrychium Virginianum 

 the germinating spore develops chlorophyll would point to this. 



Apogamy, or the development of the sporophyte from the 

 prothallium as a vegetative bud, was first discovered by Farlow ^ 

 and later investigated by De Bary,'* Leitgeb,^ and Sadebeck." 

 It is known at present in Pteris Cretica, Aspidiinn filix-vias 

 var. cristatum, Aspidium falcatum, Todea Africana, and several 

 others. Sometimes archegonia are produced, or they may be 

 absent from the apogamous prothallium, but antheridia usually 

 are found. When archegonia are present they do not appear 

 to be functional. In Pteris Cretica, where usually no archegonia 

 are developed, the cushion of tissue which ordinarily produces 

 them is formed as usual ; but instead of forming archegonia it 

 grows out into a leaf at whose base is formed the stem apex, 

 which soon produces a second leaf. The first root arises 

 endogenously near the base of the primary leaf, and the young 

 plant closely resembles the sporophyte produced in the normal 

 way. Previous to the development of the bud there is formed in 

 the prothallium itself a vascular bundle which is continued into 

 the leaf, but which is entirely absent from normal prothallia. 



The opposite state of affairs, where the gametophyte arises 



1 Goebel (i). '^ Goebel (10), p. 245. ■' Farlow (i). 



'■ De Bary (2). ^ Leitgeb (13). s Sadebeck (6), p. 231. 



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