98 
GENETICS: E. M. EAST 
starting to grow at the same rate as the others, pass down the style 
faster and faster, until they reach the ovary in four days or less. 
From these facts it seems reasonable to conclude that the secretions 
in the style stimulate the pollen-tubes from other plants instead of in- 
hibiting the tubes from the same plant. 
The whole question, therefore, becomes a mathematical one, that of 
satisfying conditions whereby no stimulus is offered to pollen-tubes from 
the same plant, but a positive stimulus is offered to tubes from nearly 
every other plant. 
The nearly constant rate of growth of pollen-tubes in the pistils of 
selfed flowers, compared with the regular acceleration of growth of the 
tubes from the pollen of other plants, undoubtedly shows the presence 
of stimulants of great specificity akin to the 'Individuals toff e' of Jost, 
though I believe their action to be indirect. Experiments by several 
botanists, which I have been able partially to corroborate, point to a 
single sugar, probably of the hexose group, as the direct stimulant. The 
specific 'Individualstoffe' I believe to reside in the pollen grains and to 
be in the nature of enzymes of slightly different character, all of which 
except the one produced by the plant itself for the use of its own pollen, 
or by another individual of the same genotype, can call forth secre- 
tion of the sugar that gives the direct stimulus. At least this idea 
links together logically the fact of the single direct stimulus and the 
need of 'Individualstoffe' to account for the results of the crossing and 
selfing experiments But whether or not this be the correct physiologi- 
cal inference, the crossing and selfing experiments call for an hypothe- 
sis that will account for no stimulation being offered the tubes from the 
plant's own pollen while at the same time great stimulation will be given 
the tubes from the pollen of nearly every other plant. This is a straight 
mathematical problem, and it is hardly necessary to say that it is in- 
soluble by a strict Mendelian notation such as Correns sought to give. 
This is obvious to anyone familiar with the basic mathematics of Men- 
dehsm. On the other hand a near Mendelian interpretation satisfies 
every fact. 
Let us assume that different hereditary complexes stimulate pollen- 
tube growth and in all likelihood promote fertilization, and that like 
hereditary complexes are without such effect. One may then imagine 
any degree of heterozygosis in a mother plant and therefore any degree 
of dissimilarity between the gametes it produces, without there being the 
possibihty of a single gamete having anything in its constitution not 
possessed by the somatic tissues of the mother plant. From the chromo- 
