228 University of California Publications in Agricultural Sciences [Vol. 7 



length. Soil also had a great influence in their experiments in deter- 

 mining the size of the flowers. ' * The conclusion seems irresistible that 

 flower size in Nicotiana is not so constant as it has been assumed to be, 

 but that it is affected by a number of conditions and that at least 

 some of these may not affect the length and spread in the same 



manner. ' ' 



Influence of Age of Plant 



In Crepis capiUaris, the 25 capitula first formed are usually very 

 uniform and show a very narrow range of variation. The terminal 

 flower is usually the largest, although the next two flowers below it 

 are of the same size in manj^ instances; but usually there is a signifi- 

 cant difference of 1 mm. when a large number of flowers are measured. 

 The flowers were pulled off and measured in every instance, which 

 eliminated to a large extent the possibility of the flowers' growing 

 slightly smaller. As a rule the 25 flowers required were measured in 

 about a week's time, although the plant normally continues to flower 

 for about four to five weeks. Flowers measured at the end of a season 

 are about 15 to 20 per cent smaller than those measured at the begin- 

 ning and, owing to the setting of seed and senility of the plant, all 

 the buds formed do not open. In an experiment which was carried 

 on to measure the entire lot of flowers that were produced on 6 plants 

 of a strain, the plants started flowering on the tenth of February and 

 continued till the end of April. Comparing the early flowers with 

 those formed later, the size of the latter is smaller. But this reduction 

 is not so great as in the case of plants from which no flowers are 

 removed. Two things can be noted, however, in the flowers formed 

 later. The number of flower heads that open on any given day is less 

 than before and the number of florets per head is significantly smaller, 

 the capitulum showing a more open center. The actual size of the 

 floret is not perceptibly reduced and this accounts for the fact that 

 the size of the flowers remains fairly constant. Another character 

 that can be seen in the flower heads formed later is the slender elon- 

 gated stalks on which they are borne as compared with the robust stalks 

 of the earlier formed flower heads, while in many cases the internodes 

 between the flower stalks are longer in the later formed flowers. 



