RECENT WORK ON MOSSES AND FERNS. 367 



embryology, a very strong body of rebutting evidence 

 appears to oppose the recognition of affinity of Mosses 

 and Filmy Ferns on the basis of the plastic gameto- 

 phyte. 



The Ferns form a natural series (Bower, Annals of 

 Botany, vol. iii., 1889). At the one end we find the 

 eusporangiate types with massive meristems and sporangia, 

 the latter being often associated to form synangia ; the 

 sexual organs are deeply sunk. At the other end of the 

 series are the Leptosporangiate types, with more definite 

 segmentation of the meristems* attenuated and separate 

 sporangia, and projecting sexual organs. The peculiar 

 parallelism of all these characters indicates that the series is 

 probably a natural one. The question will be, which are 

 the more primitive forms ? The only direct evidence is 

 from the rocks, and however insufficient this may be, it 

 points clearly to an early preponderance, if not even an 

 actual priority of the eusporangiate type. With this are to 

 be coupled other considerations : — 



( 1 ) That as the Leptosporangiate Ferns are the only 

 plants with sporangia originating from a single cell, and 

 since the Lycopods and Equiseta are probably quite distinct 

 stocks, the probability of some at least of the eusporangiate 

 forms having been primitive is a strong one. 



(2) That an increasing complexity of form was certainly 

 a leading feature of the progression from any Bryophyte 

 to any Pteridophyte, and the steps from a synangial sorus 

 to a sorus with separate sporangia would have involved a 

 similar increase of complexity of form ; it would be a progres- 

 sion in harmony with the general spirit of the advance. 



(3) That those who uphold the Leptosporangiates as 

 primitive have not yet given any reasonable explanation 

 of how that condition came into existence. 



(4) That the hypothesis of septation resulting in syn- 

 angia is in accordance with developmental data ; it is 

 analogous to what is actually seen in the septate anthers 

 of Angiosperms, and it is clearly foreshadowed in the 

 Anthocerotese. We are therefore able to give a reasonable 



suggestion how synangia may have arisen. 



26 



