420 



University of California Puhlicationa in ArjricuKuraJ Sciences [Vol. 



the taraxacifolia X teciornm hybrid, while the percentage of irregu- 

 larities in meiosis II was nearly as large. In other words, the last 

 two hybrids, one involving diflTerent subgenera and the other, different 

 sections of the same subgenus, display much greater irregularity 

 during meiosis in their jioUen mother cells than does the hybrid 

 between two species of the same section. 



Data on the proportion of ai)parently good pollen grains formed 

 are in close agreement with the foregoing. Pollen counts of 500 to 

 1000 grains per plant were made in most cases. The pollen was 

 stained with acetocarmine and showed great variation in size and 

 staining capacity of the grains. Only those grains of average or large 

 size and deeply stained were counted as "good." In the case of 

 C. aspera X acnleata three plants gave 36, 40, and 48 per cent respec- 

 tively of good pollen. Of the taraxacifolia X tecforum hybrids three 

 plants had from 1 to 2 per cent of good grains. Only one plant of 

 aspera X hursifolia Avas examined and it gave less than 1 per cent 

 of good pollen. Fortunately, however, pollen counts were made on 

 three plants of hursifolia X acnleata and two plants of taraxacifolia 

 X aspera and all these gave onl}^ 1 per cent or less of good pollen. 



The proportion of viable egg cells produced in Crepis hybrids is 

 usually larger than the proportion of viable pollen formed. The only 

 data bearing on this in the three hybrids discussed above are Haney's 

 observations on the amount of open-pollinated seed produced, and 

 under conditions at Berkeley this is rather variable. The observa- 

 tions made, however, indicate general agreement between amount of 

 open-pollinated seed produced and proportion of good pollen grains 

 present. 



The data on meiosis, pollen formation, and fertility nia.\- be .sum- 

 marized as follows: 



