8 Proceedings of the Royal Irish Academy. 



figui'es the daughter chromosomes (with one exception to he referred 

 to later on) vei-tically over one another. So far as my otto experience 

 goes, the daughter chromosomes in the great majority of cases are in 

 reality laterally displaced one over the other to the extent shown in 

 figs. 7 and 18. This lateral displacement is, howeyer, much smaller 

 than requii-ed hy Gregoire's scheme, and is in fact just the thickness of 

 one limh of the V-shaped chromosomes ; so that the ends of one V lie 

 beside those of the sister chromosome just before leaving the equatorial 

 plate. This displacement of the daughter chromosomes "vrith regard 

 to one another may be seen in the figures of several investigators, e.g. 

 in those of Miss. Sai'gant,^ Strasbui'ger and [Mottier,- and indistinctly 

 in one by Gregoire, himself the figure before alluded to.^ 



In all these figures the ends of the daughter chromosomes lying in 

 the equatorial plane overlap, and are interlaced and present an appear- 

 ance, which, I believe, could only be produced by the formation 

 of each of the V-shaped daughter chromosomes from half of both 

 portions of the original twisted chromosomes of the equatorial plate, 

 each limb of the V being a longitudinal half of one portion. 



In order to make the process clear, as I conceive it, reference to 

 the accompanying diagrams will be necessary : — Fig. 12 represents 

 diagrammatically a chromosome di:fferentiatcd fi'om the strepsi- 

 nematous thread. It is composed of two portions twisted on each 

 other, and each portion is a segment of the original dolichonematous 

 thread, and has been brought into juxtaposition with a similar segment 

 of the same thread and twisted round it. In the same diagram one 

 of these portions is marked with spots and one with circles. A 

 longitudinal division is also shown running down each portion. For 

 the sake of clearness one half of one portion is marked with larger, and 

 the other half with smaller circles. Similarly the adjacent portion is 

 longitudinally divided into an half marked with large and an half 

 marked with small spots. This longitudinal division has been recorded 

 by several writers. In fig. 12 is represented the structure of a chro- 

 mosome, with four free ends, such as is figured in fig. 3 and 4, while in 

 fig. 13 is shown the structru'e of the common looped form of chromo- 

 some. For the sake of description we will designate each twisted 

 portion {i.e., that marked with circles or spots) of the double chromo- 



1 Ann. of Eot., Sept. 1896, fig. 23 ; and June, 1897, fig. 13. 

 -Ber. d. deutsch. bot. Ges. 1897 Taf. xv., fig. 1; and Mottier. Jahrb. f. 

 wiss. Bot. 1897. Taf. iii., 15. 

 ^Loc. cit, fig:. 21. 



