crossed, at least occasionally, by pollen from a distinct plant.
Sprengel at times foresaw this law, but only partially, for it does not
appear that he was aware that there was any difference in power between
pollen from the same plant and from a distinct plant. In the
introduction to his book (page 4) he says, as the sexes are separated in
so many flowers, and as so many other flowers are dichogamous, "it
appears that nature has not willed that any one flower should be
fertilised by its own pollen." Nevertheless, he was far from keeping
this conclusion always before his mind, or he did not see its full
importance, as may be perceived by anyone who will read his observations
carefully; and he consequently mistook the meaning of various
structures. But his discoveries are so numerous and his work so
excellent, that he can well afford to bear a small amount of blame. A
most capable judge, H. Muller, likewise says: "It is remarkable in how
very many cases Sprengel rightly perceived that pollen is necessarily
transported to the stigmas of other flowers of the same species by the
insects which visit them, and yet did not imagine that this
transportation was of any service to the plants themselves." (1/4. 'Die
Befruchtung der Blumen' 1873 page 4. His words are: "Es ist merkwurdig,
in wie zahlreichen Fallen Sprengel richtig erkannte, dass durch die
Besuchenden Insekten der Bluthenstaub mit Nothwendigkeit auf die Narben
anderer Bluthen derselben Art ubertragen wird, ohne auf die Vermuthung
zu kommen, dass in dieser Wirkung der Nutzen des Insektenbesuches fur
die Pflanzen selbst gesucht werden musse.")

Andrew Knight saw the truth much more clearly, for he remarks, "Nature
intended that a sexual intercourse should take place between
neighbouring plants of the same species." (1/5. 'Philosophical
Transactions' 1799 page 202.) After alluding to the various means by
which pollen is transported from flower to flower, as far as was then