upon which the growth of the plants has been modified. If so, and only
on that condition, it would follow that when all the measurements,
either of the crossed or the self-fertilised plants, were combined into
a single series, that series would be statistically regular. The
experiment is tried in Table 1/1, columns 7 and 8, where the regularity
is abundantly clear, and justifies us in considering its mean as
perfectly reliable. I have protracted these measurements, and revised
them in the usual way, by drawing a curve through them with a free hand,
but the revision barely modifies the means derived from the original
observations. In the present, and in nearly all the other cases, the
difference between the original and revised means is under 2 per cent of
their value. It is a very remarkable coincidence that in the seven kinds
of plants, whose measurements I have examined, the ratio between the
heights of the crossed and of the self-fertilised ranges in five cases
within very narrow limits. In Zea mays it is as 100 to 84, and in the
others it ranges between 100 to 76 and 100 to 86."

"The determination of the variability (measured by what is technically
called the 'probable error') is a problem of more delicacy than that of
determining the means, and I doubt, after making many trials, whether it
is possible to derive useful conclusions from these few observations. We
ought to have measurements of at least fifty plants in each case, in
order to be in a position to deduce fair results. One fact, however,
bearing on variability, is very evident in most cases, though not in Zea
mays, namely, that the self-fertilised plants include the larger number
of exceptionally small specimens, while the crossed are more generally
full grown."

"Those groups of cases in which measurements have been made of a few of
the tallest plants that grew in rows, each of which contained a