CHAPTER 10 



APOGAMOUS FERNS. THE GENERAL 



PHENOMENON 



It may now perhaps be appropriate to consider a little more closely some of the remark- 

 able cytological peculiarities accompanying obligate apogamy in the Polypodiaceous 

 ferns. Some examples of this type of life history have already been introduced incident- 

 ally when describing Dryopteris Borreri, Phegopteris and others, but the peculiarity is not 

 confined to members of the Dryopteroid affinity. It has been met with from time to 

 time in widely scattered genera, in each of which it must have arisen de novo, yet the 

 main characteristics wherever they occur are so similar that all the known cases may 

 profitably be dealt with together. 



The characteristics of this particular type of life history are that in spite of the 

 existence of normal-looking and fully functional spores, the prothalh which develop 

 from them are devoid of archegonia though antheridia may be, and usually are, 

 present in abundance. A sexual fusion takes no part in the initiation of the new sporo- 

 phyte which is formed directly from the central tissue of the prothallus at a stage of its 

 development which, in a sexual gametophyte, would just precede the thickening of the 

 central cushion. The first leaf of the new sporophyte is in most cases of a more adult 

 type than is the first leaf of a sexually produced young plant, but otherwise the only 

 additional external difference that can easily be detected is that the sporangia from 

 which the functional spores are derived contain 32 spores instead of the customary 64. 



A list of species in which this type of life history is known to me is as follows : 



Pteris cretica L. 



Cyrtomium falcatum Presl 



C. Fortunei ] .Sm. = ' Aspidium falcatum' 



C. caryotideum (Wall.) Presl 



Dryopteris Borreri Newm. = ' Nephr odium pseudomas' and also many varieties referred 

 to 'Z). Filix-mas' 



D. remota (A.Br.) Hayek 



D. atrata (Wall.) Ching = ' Nephrodium hirtipes' 



Phegopteris polypodioides Fee 



Pellaea atropurpurea (L.) Link 



Asplenium monanthes L. 



All of these species have been available to me for study, and though the hst will 

 certainly be found to be incomplete with regard to ferns as a whole, most of which have 

 never been examined from this point of view, the series is sufficiently wide to be a fair 

 sample of the general phenomenon. That many species should be reviewed by one 

 person is perhaps of importance in that a number of incomplete accounts of single 

 species have been produced at various times since the discovery of apogamy by Farlow 



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