ALTERNATION OF GENERATIONS 143 



discovery that in certain ferns the sporophyte might 

 arise vegetatively from the gametophyte without the 

 formation of any archegonia ; this phenomenon Farlow 

 termed ' ' apogamy . ' ' Pringsheim thereupon experimented 

 on Mosses, and obtained protonemata, or vegetative 

 regions of the gametophyte, as buds from the seta of the 

 sporocarp, and this was later termed " apospory." These 

 discoveries led Pringsheim in 1877 to formulate the view 

 that the two stages gametophyte and sporophyte in 

 the Bryophyta, were homologous, seeing that one could 

 give rise to the other by purely vegetative methods, and 

 that sporangia were consequently homologous with 

 archegonia and antheridia. The chief point of difference 

 between Bryophyta and Thallophyta, so far as alternation 

 was concerned, would thus be that in the former the 

 series of recurrent sporophytes present in the latter 

 was reduced to one which had become parasitic on the 

 gametophyte. 



Celakowski (as interpreted by Sachs) and Pringsheim 

 were in this way the pioneer leaders of two opposing 

 schools in the interpretation of alternation of generations ; 

 as to the facts of course there was unanimity of opinion. 

 In his reply to Pringsheim in 1878 Celakowski introduced 

 the idea of the sporocarp of the Archegoniatae as a newly 

 interpolated generation between the sexual and asexual 

 generations of the Thallophyta, and this concept of an 

 interpolated phase was fully elaborated at a later date 

 by Bower, though in a somewhat different sense. 



As Bower's theory in its original form is the one that 

 has been very generally accepted it will be necessary for 

 you to study it somewhat in detail. It is formulated 

 in a long series of most important monographs in the 

 Transactions of the Royal Society and in the Annals of 

 Botany, from about 1890 onwards, and restated in a 

 more compact and accessible form in his book, The 

 Origin of a Land Flora, published in 1908. 



You are already acquainted with the fact that in the 



