1928] Wexelsen: Chromosome Numbers and Morplwlogy in Trifolium 357 



Nawaschin's fixative. Most of the plates were stained with Haideii- 

 hain's iron-haematoxylin, a few with iodine-gentian-violet (Huskins, 

 1927). For Trifolium the following procedure was found to be the 

 best: (1) Root tips: 70 per cent alcohol; iodine (5-10 min.) ; gentian 

 violet (5-10 min.) ; iodine (30 sec). (2) Pollen mother cells: 70 per 

 cent alcohol; gentian-violet (5-10 min.) ; iodine (30 sec). 



Attempts were made to study the reduction division in pollen 

 mother cells by the aceto-carmine method, but with no success. It is 

 difficult to get the anthers out of the small buds and they are filled 

 with inclusions (starch?) which apparently prevent the absorption 

 of the fixative. The methods of emasculation and pollination will be 

 described in the section on "Attempts at species crossing." 



CHROMOSOME NUMERS AND MORPHOLOGY 



Chromosome Numbers 



Martin (1924) counted the chromosomes in Trifolium pratense 

 and T. repens and found the number in both to be 12, haploid. 

 Karpechenko (1925) examined the chromosomes in somatic cells — 

 root tips — of twenty-four species and found the following series of 

 diploid chromosome numbers: 



Diploid number of chromosomes 14 16 32 48 about 80 about 130 

 Number of species 8 12 1 1 1 1 



Bleier (1925) studied the reduction division in eighteen species and 

 found the following series of haploid chromosome numbers : 



Haploid nvimber of chromosomes 7 8 9 14 16 48 

 Number of species 5 8 1(?) 2 — 2 



I have obtained chromosome numbers in ten native American species 

 with the following distribution in the groups given by McDermott 



(1910). 



Section I. Tridentatae 



2n 



T. ohtusifloi'um Hook., 2 strains 16 



T. ohtusdflorum var. majus {T. majus Greene) 16 



Section II. Variegatae 



T. variegatum Nutt 16 



T. wormskjoldii Lehm 48(?)* 



* But little material was available for fixation and the chromosomes were much 

 crowded in the cells, so that the number could not be obtained with certainty. 

 There are in figure Ic 47 bodies, one of which probably represents 2 chromosomes ;: 

 48 is very probably the correct number of chromosomes present. 



