138 Number of Chromosomes in Lathyrus 



kingdoms, the chromosome members of closely related forms are found 

 to be themselves related ; i.e. either entirely alike, or multiples of a 

 cardinal number characteristic of the group — as I have explained in my 

 work above quoted. 



The chromosome number seven is a comparatively low value to find 

 among phanerogams, and should, a priojH, count in favour of the employ- 

 ment of Lathyrus in genetic experiments. The theory as to agreement 

 between reduction division and Mendelian segregation permits — com- 

 mencing either with self-fertilisation of one heterozygotic individual or 

 by crossing of two pure lines — that there be found at the outside seven 

 independently segregating pairs of factors (or pairs of factor groups). A 

 segregation experiment commenced in one or other of these two ways 

 should not lead to the production of more than 128 different biotypes, 

 all homozygotic throughout. 



As to how far it may prove possible to find more than seven inde- 

 pendently segregating pairs of factors or pairs of factor groups in a 

 single biotype of the species, is a question which future investigations 

 must decide. Personally I feel confident that they will not be found. 



I have observed nothing in my material which might lead to the 

 interpretation that chiasmatypy, in the sense of Janssens, is met with in 

 Lathyrus. In my opinion, even in organisms in which breeding experi- 

 ments have resulted in the view that parts of the chromosomes are 

 exchanged during the reduction division, this process is not usually 

 going on at so late a stage as shown by Janssens. More probably it 

 occurs in synapsis where it cannot readily be demonstrated by micro- 

 scopical methods. 



Carlsberg Laboratorium, Copenhagen, 

 15 October 1918. 



EXPLANATION OF PLATE V. 



All figures are drawn with aid of Abbe's camera lucida, using Zeiss' homog. immers. 

 2 mm. and comp. oc. 18. 

 Figs. 1 — 7, Lathyrus odoratus. Figs. 8 — 10, L. latifolius. 

 Figs. 1 — 2. Pollen mother cell. Hetero typical metaphase (polar view). 

 Fig. 3. Pollen mother cell. Heterotypical meta-anaphase (side view). 

 Fig. 4. Two chromosomes from heterotypical anaphase (schematically). 

 Fig. 5, Pollen mother cell, Heterotypical anaphase (polar view). Apparently 7 groups 



of 4 chromosomes present. 

 Fig. 6. Pollen mother cell. Homotypical metaphase. 

 Fig. 7. Somatic cell with 14 chromosomes. 



Fig. 8. Pollen mother cell. Heterotypical metaphase (polar view). 

 Fig. 9. Pollen mother cell. Heterotypical metaphase (side view). 

 Fig. 10. Somatic cell with 14 chromosomes. 



