Tlie Royal Soi-iety, London. 



73 



theiiisclvcs, but lu-quire a more ^encral importance from tlic 

 j)ossil)ility that thcir study may tlirow liglit oii the naturc of 

 alternation of g;enci'ations in arclit'fi;oniate plants. Tlicy liave beon 

 considered tVom tliis poiiit of" view by Pr i ngslici m , and by 

 thosc wlio, following him, regard thc two gencrations as honio- 

 logous with onc another in the scnsc tliat tlic s|)oropliyte arosc 

 by tlic gradual modification of individiials originally rcsembling 

 thc sexual plant. Gel ako vsky and Bo wer, on thc other band, 

 maintain thc view that the sporophyte, as an interpolated stagc 

 in thc lifc history arising by elaboration of thc zygotc, is not the 

 homologue of thc ganictophyte , and is only rcprcsented in a fcw 

 thallophytcs. In thc light of thc theory of antithetic alternation 

 no wcight is attached to apoganiy and apospory for phylogenctic 

 })urposes. 



In thc paper of whicli this is an abstract thc rcsults obtained 

 by cultivating thc pruthalli of a numbcr of species of Ferns undor 

 conditions slightly differcnt from thc natural ones are deseribed, 

 and thcir bearing on thc problcm of the naturc of alternation 

 considered. Thc behaviour of Scolopendrium vidgare Sm. and 

 Nephrodiinn düatatum Desv., in whicli sporangia were borne upon 

 the prothallus, has already becn deseribed in a preliniinary 

 Statement.*) It is therefore sufficient to express the rcsults of 

 prolonged cultivation of these and the remaining species in a 

 tabular form. 



Table of the Rcsults of cultivating Prothalli for a Period of Two 

 Years and a Half. 

 (Note. In every species normal embryos were produecd when 

 conditions permitted fertilisation.) 



Name. 

 Scolopendrium vulgare Sm. va 

 ramulosissimum. 



Kesult. 

 Gametophytic budding^. 

 Development of archegonial projections. 

 Developmont of cylindrical process usually 

 from tlie apical region of the protliallus. 



Tracheides in cylindrical process. 

 Leaves, roots, and ramenta on 

 process. 

 Apogamy. ^ Sporangia on the process. 



Vegetative buds from tip of 

 cylindrical process, or in place 

 of an archegonial projection. 

 var. marginale. Simular to var. ramulosissimum, but no spor- 



angia, isolated ramenta, or leaves found. 

 Nephrodium dilatatum Desv. var. Gametophytic budding. 



cristatum gracile. Development of archegonial projections. 



Development of cylindrical process, usually 

 from the under surface just behind the 

 apex, which formed a „middle lobe". 



Tracheides in middle lobe and 



cylindrical process. 

 Sporangia, sometimes associated 

 with ramenta, on middle lobe 

 and process. 

 No vegetative buds. 



Apogamy. 



*) Royal Society Proc. Vol. LX. p. 250. 



