1903.] 



On the Cytology of Apogamy and Apospory. 



453 



" On the Cytology of Apogamy and Apospory. — 1. Preliminary 

 Note on Apogamy." By J. B. Farmer, F.R.S., J. E. S. Moore, 

 and Miss L. Digby. Received March 24, — Read March 26, 

 1903. 



The phenomena of apogamy and apospory have always heen regarded 

 as "short cuts" in the life history of ferns, and the fact that 

 apparently either generation may be directly produced from > the 

 other, without the intervention of oosphere or spore respectively, has 

 been taken to indicate that the gametophyte and sporophyte are 

 homologous phases in the life histories of these plants. But since the 

 cytology of the two generations has been carefully studied, it has 

 become recognised that the prothallial generation is composed of cells, 

 the nuclei of which possess only half the number of chromosomes 

 that are characteristic of the alternate sporophyte generation. 



In normal cases the doubling of the number of the chromosomes is 

 effected during the transition of the gametophyte to sporophyte by 

 the addition of the chromosomes belonging to the spermatozoid to 

 those of the oosphere, and this double number is retained until they 

 once more become reduced to one half in the formation of the spores 

 that introduce again the gametophyte stage of the life-cycle. 



It is obviously therefore of considerable theoretical interest to 

 ascertain how the irregular transitions known as apospory and 

 apogamy are effected. It is with the facts of apogamy that we are 

 here concerned, the details relating to apospory being reserved for a 

 future communication. 



Certain species of nephrodium (e.g., iV. pseudo-mas, var. polydadylwm) 

 are known to produce prothallia on which the apogamous formation 

 of sporophytes is of normal instead of rare occurrence.* By the 

 kindness of Dr. Lang we received a number of prothallia in all stages 

 of growth in which the special apogamous developments could be 

 perfectly traced. An examination of them has resulted in the dis- 

 covery of remarkable nuclear changes that appear to be obviously 

 related to the apogamy of the prothallia in question. 



If very young prothallia are examined before any apogamous 

 growths have begun to manifest themselves, it will be seen that cells 

 not unfrequently occur in which two nuclei are present. This fact 

 Avas recorded by Lang in the case of older prothallia, and was also 

 figured by Heimf in the case of Doodya caudata, but he makes no 

 mention of it in the body of his paper. 



* Lang, "On Apogamy and tie Development of Sporangia upon Fern Pro- 

 thallia," 4 Phil. Trans.,' series B, vol. 190, 1898, p. 214. 



f Carl Heim, " Untersuchungen ii. Farn Prothallien," 'Flora,' rol. 82, 1896, 

 p. 338, fig. 7. 



