334 SCIENCE PROGRESS. 



of tracheides in the prothallus may also be mentioned 

 here. 1 



The relation which exists in some cases between apos- 

 pory and apogamy on the one hand, and the much more 

 common phenomena of sporophytic and gametophytic bud- 

 ding on the other deserves to be referred to in passing ; 

 further facts are required before any definite conclusions 

 can be drawn. Certain examples of sporophytic budding 

 have been regarded as extreme cases of apogamy resulting 

 in the entire omission of the sexual generation from the life 

 cycle. 2 In no case, however, does the evidence in favour of 

 this interpretation seem to be sufficient. No really satis- 

 factory cases of apogamy or apospory occurring in ferns in 

 the natural state have yet been recorded. Apospory in 

 Pteris aquilina? on the prothalloid growths of which sexual 

 organs were not observed, and the case of the occurrence of 

 tracheides in a prothallus of Botrychium virginianum 4 were 

 observed in wild plants. A number of aposporous and apo- 

 gamous ferns are descended from wild finds, but in them it 

 is uncertain whether the peculiarity has not been acquired 

 under cultivation. 



Treub b has recently recorded a case of apogamy in an 

 Angiosperm (Balanophora elongata Bl.), the embryo of which: 

 develops without fertilisation from cells of the endosperm. 

 The details of this interesting observation will be referred 

 to below. 



NUCLEAR DIFFERENCES BETWEEN THE ALTERNATING 



GENERATIONS. 6 



The recognition of a difference between the nuclei of 

 the cells of the sexual and asexual Generations constitutes 



1 Mercklin, p. 54. 2 Goebel (1). 3 Farlow (2). 



4 Jeffrey. 5 Treub (2). 



6 No attempt has been made to give a complete list of the literature- 

 relating to the reduction of chromosomes in plants, and only those papers 

 which are necessary to illustrate the bearing of the general result on alterna- 

 tion are mentioned. Full references will be found in Strasburger (2) and. 

 (3) and in Zimmerman, Morphologie u. Physiologic d. pflanzlichen Zell- 

 kernes. 



