1920] BahcocTc-CoUins : Crepis capillaris X C. tectorum 197 



seven chromosomes, the sum of the haploid numbers of capillaris and 

 of tectorum. Nothing can be learned of the reduction division 

 because the plants never reached maturity, but there seems to be no 

 difficulty in somatic division, all seven of the chromosomes dividing 

 in an apparently normal fashion. 



Examination of a young F^ seedling (Z5) which had reached 

 the limit of development, revealed a most unusual teratological cell 

 condition (pis. 37 and 38). The tissue systems of the plant were in 

 a chaotic condition. Patches of embryonic tissue were distributed 

 here and there among the larger vegetative cells, patches or sections 

 of tracheary cells were likewise distributed here and there throughout 

 the mass. Groups of vegetative cells were separated by streaks of 

 disorganized and disintegrated tissue. It apeared as if the force that 

 directs the organization and coordination of cell systems, whatever it 

 is, was lacking. This lack of order in the cell systems prevented the 

 functioning of these systems and caused cessation of development. 



The principal features of the interspecific hybrids here recorded 

 are: 



1. Reciprocal crosses are equivalent. 



2. Fi shows dominance of tectorum cotyledon characters and hybrid 

 vigor, as expressed by the increased size of the seedling parts. 



3. Absence of complete organization and coordination of the func- 

 tioning systems, which absence causes the death of the plant at the 

 end of the cotyledon stage. 



The possible origin of species having a larger chromosome number 

 from species having a smaller number by fragmentation or segmenta- 

 tion of some of the latter has been suggested a number of times. Metz"' 

 shows a diagrammatic gradation of chromosome numbers for different 

 species of Drosophila. Hance" applies the same idea to the origin of 

 chromosome number variations in Oenothera species. Rosenberg^ 

 recently concluded that the origin of Crepis species with three, four, 

 and five pairs of chromosomes could best be explained by non-dis- 

 junction occurring during the reduction division. Bridges^ actually 



5 Metz, C. W., "Chromosome Studies in the Diptera, I. A prelimiiiMry study 

 of five different types of chromosome groups in the genus Drosophila. ' ' Jour. 

 Exp. Zool., vol. 17 (1914), pp. 45-59. 



c Hance, E. T., "Variations in the number of somatic chromosomes in 

 (Enothera scintillans de Vries. " Genetics, vol. 3 (1918), pp. 225-261. 



■^ Rosenberg, O., ' ' Chromosomenzahlen und Chromosomendimensionen in der 

 Gattung, Crepis." ArMv for Botanik, Bd. 15 (1918), p. 11 . 



8 Bridges, C. B., "Non-disjunction as proof of the chromosome theory of 

 heredity." Genetics, vol. 1 (1916), pp. 1-52 and 107-163. 



