1881.] | by the Ftstory of Sex in Plants. 95 
experiments is that some of them actually do show a clear differ- 
ence in favor of cross-fertilization, It may be compared to the 
attempt of astronomers to obtain the parallax of a fixed star. 
The result is in the highest degree satisfactory if it is certain that 
any positive angle is measured. And, as in the astronomical 
parallax, the greatest exactness is required to measure the vast- 
ness of space and its contents, so in the biological parallax 
equally great precision is needed to measure the vastness of time 
and its effects. 
Independently of insect agency, however, the vegetable king- 
dom furnishes many facts which prove the unstable state in 
which the sexual relations are still found to exist. 
In many cases it is difficult to determine whether the move- 
ment is at the present time towards a greater or a less degree of 
separation. In a former paper read before this Association’ I 
endeavored to bring forward the evidence to prove that certain 
species of Lauraceze, and notably the genera Sassafras and Lin- 
dera, had already passed through three different stages, of which 
traces are still left in the form of “rudiments” or obsolete organs. 
In this case the movement has obviously been towards more 
complete sexual separation. In the majority of other common 
cases, such as Smilax, Ilex, Rumex, Rhus, Chamelirium, &c., 
where the rudiments of both stamens and pistils remain, though 
one or the other set is functionless and the plants are really 
dicecious, the direction of development seems also to be towards 
sexual distinctness, and it may well be doubted whether the | 
flowers of the oak, the alder, or the willow were ever hermaphro- 
dite. Still, progress toward hermaphrodism may also be going 
on in some species where insect fertilization is found a sufficient 
substitute for the distinction of sex. 
Upon the whole, however, it must be concluded that the special 
effect of the appearance of insects in the Mesozoic or Secondary 
age of geology was to render the evolution of new hermaphrodite 
forms possible, which vastly enriched the world’s flora, since prior 
to that time only diclinous species could survive, and that this 
great army of plants, having been thus brought into existence in 
this imperfect condition, have since been gradually throwing off 
their encumbrance, and at different rates moving orvam toward 
sexual independence. 
* Published in the Scientific American Supplement of Sept. 20, 1879, p. 3089. 
