544 



THE PURE LINE HYPOTHESIS. 



During December, 191 5, and January, 191 6, only 17 seeds 

 were obtained, owing to the fact that many of the flowers failed 

 to set seed. It was quite clear that fertility was much impaired 

 by self-fertilisation. The 17 seeds were sown on 31st January, 

 1916, and only seven germinated. These seven offspring were 

 grow^n to maturity. They were all dwarf plants like the parent, 

 all had variegated leaves, and all had red flowers. On placing the 

 flowers in alcohol, those of four plants became colourless, those 

 of two became deep yellow, and one plant was not tested. 



2. Female or Seed-Plant (B). 



At the same time there was growing in a garden about three- 

 quarters of a mile from the Museum a tall nasturtium plant with 

 climbing, sprawling habit. The leaves were large and uniform 

 green, the flowers were pale yellow wath chromoplasts absent. A 

 number of flowers were self-fertilised, and 34 seeds were obtained. 

 These were sown on 3i|St January, 1916, and 20 germinated. The 

 mature plants were all non-variegated, and were tall, sprawling 

 plants. In 16 plants the flowers were pale yellow (no chromo- 

 plasts) like those of the parent, in two light red without chromo- 

 plasts, in one deep yellow (owing to abundance of chromo- 

 plasts) with an occasional blush of red on some of the flowers, 

 and in one deep yellow with no red tinge. 



From these results we are led to consider that the male plant 

 was homoz3'gous with regard to dwarf habit and variegation, and 

 the female plant with reference tO' tall, sprawling habit and 

 uniform green leaves of large size. 



The gametic nature of the parents with regard to the colour 

 of the flowers is less clear, since all three colouring substances 

 were present among different offspring arising from each parent. 



Thus the characters of redness and the presence of chromo- 

 plasts do not give a simple Mendelian relationship iir inheritance. 

 Doubtless^ with further breeding it might be possible to find 

 hypotheses involving multiple factors or the presence of inhibitors 

 which would render the experimental results intelligible; but the 

 present purpose does not necessitate any such attempt. 



3. Crossing of Nasturtium Plants A ( S ) and B ( 9 ) — Hybrids. 



The tall, pale yellow nasturtium plant (B), with green leaves, 



was crossed with the pollen of the dwarf, medium-red, variegated 



