56 Mr. W. H. Lang. On Apogamy and the 



development, so do they also present the first introduction of enamel 

 as a separate tissue. 



In its first introduction it was a joint product, made under circum- 

 stances which almost precluded any slow and gradual formation of 

 an outer layer upon the teeth ; but in the further specialisation of 

 teeth in reptiles and mammals the tooth germs sink more deeply into 

 the submucous tissue, and are protected for a much longer time. 



The enamel organs become more specialised, and finally take upon 

 themselves the entire work of enamel building, manufacturing both 

 the organic matrix and furnishing it with lime salts, as unquestion- 

 ably happens in mammals. 



And if these conclusions be correct, it would be quite justifiable to 

 call it enamel, even though the dentine papilla has had a share in its 

 production. 



*' On Apogamy and the Development of Sporangia upon Fem 

 Prothalli." By WILLIAM H. LANG, M.B., B.Sc., Lecturer in 

 Botany, Queen Margaret College, and " G-. A. Clark " 

 Scholar, Glasgow University. Communicated by Professor 

 F. 0. BOWER, Sc.D., F.R.S. Received February 28, Read 

 March 3, 1898. 



(Abstract.) 



The two most important deviations from the normal life-history 

 of ferns, apogamy and apospory, are of interest in themselves, but 

 acquire a more general importance from the possibility that their 

 study may throw light on the nature of alternation of generations- 

 in archegomate plants. They have been considered from this point 

 of view by Pringsheim, and by those who, following him, regard the 

 two generations as homologous with one another in the sense that 

 the sporophyte arose by the gradual modification of individuals 

 originally resembling the sexual plant. Celakovsky and Bower, on 

 the other hand, maintain the view that the sporophyte, as an inter, 

 polated stage in the life-history arising by elaboration of the zygote y 

 is not the homologue of the gametophyte, and is only represented in 

 a few thallophytes. In the light of the theory of antithetic alterna- 

 tion no weight is attached to apogamy and apospory for phyloge- 

 netic purposes. 



In the paper of which this is an abstract the results obtained by 

 cultivating the prothalli of a number of species of ferns under 

 conditions slightly different from the natural ones are described, and 

 their bearing on the problem of the nature of alternation considered. 

 The behaviour of Scolopendrium vulgare, Sm., and Nephrodium- dilata- 





