86 



Mr. E. P. Gregory. 



[Jan. 5, 



" The Eeduction Division in Ferns." By E. P. Gregory, St. John's 

 College, Cambridge, University Demonstrator in Botany. 

 Communicated by Professor H. Marshall Ward, F.E.S. 

 Eeceived January 5, — Eead February 5, 1904. 



The earlier work upon the spore-formation in Ferns having led to 

 divergent results, a new investigation was begun in connection with 

 other cytological work bearing upon the Mendelian hypothesis. 

 During the progress of this work, Professor Farmer and 

 J. E. S. Moore, in their preliminary communication to the Eoyal 

 Society upon the reduction-phenomena of plants and animals,* 

 indicated the occurrence of a true reduction at the heterotype division 

 in both plants and animals. The examination of the early stages of 

 spore-formation in Ferns leaves no doubt that the essential features 

 of the phenomena described by the above-mentioned authors are 

 present also in this group of plants. 



The species which I have examined are Pteris tremida, Scolopendrium 

 vulgare, Asplenium marinum, the so-called hybrid between Scolopendrium 

 vulgar e and Asplenium ceterach, Onoclea sensibilis, Davallia capensis and 

 Fadyenia prolifera. All these are included among the Polypodiacece. 

 The processes of spore-formation are identical in all these types. The 

 reduced number of chromosomes, which appears at the heterotype 

 division, is thirty- two. f Owing to the smallness of the nuclei it is not 

 easy to determine exactly the number of the chromosomes in the case 

 of the vegetative cells, but it is about sixty, and I think there is a 

 strong presumption that the number is, as stated by Stevens, \ sixty- 

 four. 



An examination of Dicksonia davallioides and of Alsophila excelsa 

 (Cyatheacece) was sufficient to show that it is extremely probable that 

 the following description applies equally to these plants, but as the 

 quantity of material hitherto available was small, only the early stages 

 have been examined as yet. 



After the vegetative divisions of the archesporium are complete, 

 the spore mother-cells undergo a period of rest during which the 

 nuclei increase in size. At the end of this period, that is, in the 

 earliest prophase of the reduction division, the spireme thread under- 

 goes a longitudinal fission. The ensuing contraction of the spireme 

 towards one end of the nucleus results in the formation of a series of 

 loops. The double nature of the loops, which is a consequence of the 

 longitudinal fission of the thread, is clear. 



* ' Roy. Soc. Proc.,' 1903, June 18. 



f In Pteris tremula no exact counts were made, but the number is apparently 

 the same as in the other species described. 



X " Ueber Chromosomentheilung bei der Sporenbildung der Farne," ' Ber. d. 

 Deutsch. Bot. Gesellsch.,' 1898, p. 263. 



