420 The Botanical Gazette. [December, 
The ogeasional cross.—When in 1876 I addressed the meeting of the 
American Association for the Advancement of Science at Detroit,! 
taking for my text what I then regarded as an extravagance, the exact 
language of a great teacher inscience: “All plants with conspicuously 
colored flowers, or powerful odors, or honeyed secretions, are fertilized 
by insects; all with inconspicuous flowers, and especially such as have 
pendulous anthers, or incoherent pollen, are fertilized by the wind” 
I did not expect to see the proposition so widely modified as it is 
to-day. Our great leader, Asa Gray, wrote to me reiterating the 
strength of the position I was combating, and in the curt way quite 
allowable in the correspondence of friends whose regard for each other 
no difference of opinion could weaken, “dared” me to produce an 
instance of a flower as above characterized, that was not arranged for 
cross-fertilization. It was chiefly this “daring” that has led me in 
recent years to produce-the instances. The broad view soon became 
modified so as to read that the plants were so arranged as to pollinate 
themselves in many instances when insects failed to do the work, and 
I doubt very much whether there is a prominent botanist to-day, who 
will deny that-there are numerous instances in which sweet and colored 
flowers are so arranged that cross-fertilization 1s next to impossible. 
Indeed it has come to be quite frequent for authors on the relations 
between flowers and insects, when noting the contradictive facts to 
simply observe that an “occasional cross is not improbable. 
It may not be useless at this stage of the progress of thought to 
inquire, what is the physiological value of an “occasional cross”? 
No one familiar with nature can fail to see that, of the millions of 
seeds annnally produced by plants, an almost imperceptible fraction 
only come to seed bearing individuals, and the seeds from the “occa- 
sional cross” can scarcely have any record in the progressive history . 
of the race. Suppose we take Mr. Robertson’s illustration of Mol/ugo 
verticillata (p. 274). I am satisfied that the “occasional cross” never 
occurs, and that “spontaneous self-pollination may take place” 1s 
putting the case with gratuitous mildness. A microscope would show 
that not only are the pollen-sacs disrupted and the pollen discharged 
over the pistil before the flower opens; but so long that the ovarium 
has commenced to assume the brown tint of ripeness, and the seeds,with 
full cotyledons, have reached their full size. But suppose this not to 
be the case, what chance has an “occasional cross” to get the resultant 
seeds into the reproductive stage again? I have before me a single 
plant of less than average size. It is one-sided, and extends over half _ 
a circle witha twelve inch radius. I find in one seed vessel just 30 
*See Proc. Am. Ass. xxiv. Pp. 224. 
