second and more remote degrees. The relationship will thus have become
more and more inextricably complex in the later generations; with most
of the plants in some degree and many of them closely related.

I have only one other point to notice, but this is one of the highest
importance; namely, that the crossed and self-fertilised plants were
subjected in the same generation to as nearly similar and uniform
conditions as was possible. In the successive generations they were
exposed to slightly different conditions as the seasons varied, and they
were raised at different periods. But in other respects all were treated
alike, being grown in pots in the same artificially prepared soil, being
watered at the same time, and kept close together in the same greenhouse
or hothouse. They were therefore not exposed during successive years to
such great vicissitudes of climate as are plants growing out of doors.

ON SOME APPARENT AND REAL CAUSES OF ERROR IN MY EXPERIMENTS.

It has been objected to such experiments as mine, that covering plants
with a net, although only for a short time whilst in flower, may affect
their health and fertility. I have seen no such effect except in one
instance with a Myosotis, and the covering may not then have been the
real cause of injury. But even if the net were slightly injurious, and
certainly it was not so in any high degree, as I could judge by the
appearance of the plants and by comparing their fertility with that of
neighbouring uncovered plants, it would not have vitiated my
experiments; for in all the more important cases the flowers were
crossed as well as self-fertilised under a net, so that they were
treated in this respect exactly alike.

As it is impossible to exclude such minute pollen-carrying insects as