330 SCIENCE PROGRESS. 



DEVIATIONS FROM THE NORMAL MODE OF ALTERNATION 



OF GENERATIONS. 



The fact has already been mentioned that it was the 

 discovery of apospory in mosses, together with the earlier 

 discovery of apogamy in ferns, which led to the theory of 

 homologous alternation being stated. Further investiga- 

 tion has strengthened the evidence to be derived from these 

 deviations from the normal life history if — and this is still a 

 disputed point — they afford any valid evidence at all. 1 



Little further has become known of apospory in mosses 

 since Pringsheim ' 2 induced it in Hypnum cupressi forme, 

 H. Serpens and Bryum ccespitosum and Stahl ' A confirmed 

 his observations in Ceratodon purpureus. These experi- 

 ments do not appear to have been further extended, but 

 the interesting fact has been recorded 4 that a similar phe- 

 nomenon may occur in sporogonia of Funaria hygrometrica 

 while still attached to the moss plant, which was growing in 

 a natural state. The sporogonia in question were found 

 with atrophied capsules buried in the soil and giving rise 

 to protonemal filaments. Such a case approaches closely 

 to the hypothetical future development of a moss plant 

 imagined by Pringsheim in 1877. No further investiga- 

 tions have been made to determine whether the gemma- 

 like bodies found in capsules of Eucamptodon perichcEtialis b 

 were aposporously developed as seems not improbable from 

 the brief description. 



The corresponding phenomenon in ferns, anticipated 

 on theoretical grounds by Pringsheim, has been made 

 known and investigated in a number of species. Dis- 

 covered by Druery 7 in Athyrium Filix-foemina and by 

 Wollaston 8 in Polystichnm angulare, these early cases 

 were fully investigated by Bower. 9 Apospory is now 

 known in nine species, viz : — 



1 On the general question of the value of abnormalities in morphology, 

 see Goebel (6), pp. 152 et seq. 



2 Pringsheim (4), (5). 3 Stahl. 4 Brizi. 

 5 Montague. 6 Pringsheim (5). 7 Druery (1). 

 s Wollaston. 9 Bower (1), (3). 



