IQQ Pearl and Surface. 



somewhat differently towards the zero point'). After July 3 it is 

 evident that the plants in all the series are growing much more rapidly, 

 and that tliis increased rate of growth is maintained until the final 

 height is reached. Now by July 3 tassels were showing in the majority 

 of plants although these were not sufficiently advanced to measure until 

 July 6. It seems unquestionable that the increased rate of gi'owth (as 

 measured by the height of the plant) is associated with the formation 

 of the tassel. The question naturally arises as to whether the approaching 

 matuiity of the sexual organs is in any way responsible for this change 

 in the rate of growth. Thus we know that in many mammals, for 

 example man, the growth curve changes very markedly before puberty 

 leading to the so-called „pre-pubertal acceleration". Further in certain 

 plants such as the common dandelion there is a very rapid elongation 

 of the seed stem with the ripening of the seed. 



While this more rapid elongation of the internodes in the coi'u 

 plant may be influenced by the approaching maturity of the male sexual 

 elements the following facts should also be considered. At the time 

 the tassel appears practically all the leaves of the corn plant are fully 

 formed. Further, from general observation supported by a large number 

 of measurements made by ourselves, it is certain that a corn leaf never 

 grows after it is fully unfolded, and we believe that the actual growth 

 ceases some time before this. That is, the final unfolding of the leaf 

 is due to the lengthening of the internodes. Thus, with the completion 

 of the leaves, by the time the tassel emerges the growth forces are 

 directed into another channel viz., the lengthening of the internodes. 

 This explanation is simpler and will probably account for many of the 

 facts unless it can be demonstrated that the male sexual products in 

 themselves are capable of accelerating the growth. This question will 

 be referred to again in connection with the variability. 



The curves obtained from the tassel heights (series D, E and F) 

 show a still more rapid growth than the leaf measurements during the 

 same period. This arises from the fact that in measuring the tassel 

 height we are measuiing only the length of the internodes, and further 



') It will be noted that there is a slight drop in all the curves at June 19. 

 The reason for this it not clear. There were no meteorological conditions which should 

 have affected the corn adversely at this time. We find from our notes, howewer, that 

 the plots were given a hoeing on June 15 and 17. It is possible that the root pruning 

 at this time may have caused the slight drop in the curves. Tliis question will be dis- 

 cussed more fully iu connection with the variation constants. 



