FLUCTUATION 



93 



only be made with safety when the plants are equally 

 healthy. 



The stem. — The branching habit of the stem has not 

 received from the author the attention it merits. Some 

 evidence may be gleaned indirectly from the flowering- 

 curves, but systematic study of fluctuation in branching 

 is difficult,* unless a high subjective error is risked. 



The height of the central axis is easily examined. The 

 plants are measured to the nearest 5 cm. every week or 

 fortnight, taking the soil-surface and the terminal bud as 

 the approximate extremes. A portion of the fullest series 

 of height determinations obtained as yet is plotted in 

 Fig, 48. This series represents an extreme case, some 

 plants being badly stunted. The height determinations 

 in this family can be compared with similar series from a 

 very uniform lot of seedlings belonging to family " 307," 

 and also with rows of commercial Afifi plants in field crop. 

 These last were measured to bench-marks with a water- 

 level. The statistical statement is as follows : 



The fluctuation in a wide-sown pure strain decreases as 

 the plants grow older, stunts overtaking the normals. 

 This is partly the case in field sowing, though to a less 

 extent owing to competition, and it is further masked in 

 commercial varieties by their non-uniform composition. 



* See, however, Leake, H,M., 2 and 3. 



