CHAP, i The Nature of Alternation of Generations 51 



He did service, too, in emphasizing the progressive advance 

 in organization of the spore-bearing form, and in finally 

 removing from the controversy the alternation of shoots. 



It is thus seen that to Sachs we owe the first clear 

 presentation of the idea that there is a regular alternation 

 of generations in the Thallophytes, based as we have seen 

 upon his conception of the course of development of the 

 Algae and the Fungi, and of the homologies of the struc- 

 tures occurring in their life-history. As we look back upon 

 his views to-day, we seem to see him basing them upon the 

 undoubted sequence of events in the archegoniate plants, 

 and with some ingenuity, perhaps even with some straining 

 of interpretation of appearances to make them fit into his 

 scheme, finding that a single law runs through the whole 

 vegetable kingdom an instance of somewhat hasty gene- 

 ralization, though supported by many life-histories. His 

 writings suggest that very little doubt remained in his own 

 mind and that he held there was little room for discussion. 



At about the time when Sachs was thus presenting the 

 subject to his numerous readers, a discovery was made 

 which led a little later to the revival of the homologous 

 view and to its restatement and elaboration by Pringsheim. 

 This was the observation made by Farlow in 1874 that it 

 is possible for a fern plant to grow altogether vegetatively 

 from a prothallus, without the intervention of the sexual 

 organs. It seemed not unfair to argue consequently that the 

 two forms are homologous. Pringsheim, to whose \vork on 

 the Algae the controversy up to that date owed so much, 

 gave immediate attention to the study of the phenomenon, 

 which its discoverer called apogamy, and especially to the 

 possibility of obtaining the similar and supplementary pro- 

 duction of the sexual phase vegetatively from the asexual. 

 In this, after many experiments, he succeeded, cultivating 

 protonemata from the divided seta of the capsule of a moss. 

 These two phenomena, Apogamy and Apospory, naturally 



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