410 
POPULAR SCIENCE REVIEW. 
fertility of the “legitimate” unions becomes still more striking when we 
find that the average weight of seed in good capsules from legitimate and 
illegitimate unions is as 54 to 35. Thus in this first series of experiments — 
the results of which, however, are perhaps a little below the average — the 
fertility of the legitimate and illegitimate unions, as shown by percentage 
THE STAMENS AND PISTIT.S OF THE TWO FORMS OF COWSLIP, SHOWING THE FOUR 
POSSIBLE UNIONS OF THE POLLEN WITH THE STIGMAS. 
results, in weight of seeds, would seem to stand approximately in the pro- 
portion of 38 to 11 ; or, in other words, the legitimate unions are 3£ times 
as prolific as the illegitimate ones. 
The inference from these facts appears quite plain — the peculiar arrange- 
ment of the parts in the flowers of the cowslip is manifestly intended to 
insure the occurrence of cross-fertilization. The general facts must have 
been well-known to botanists for many years, seeing that the distinction of 
“ pin-eyed ” and “ thrum-eyed ” polyanthuses has long been recognized by 
florists ; but their interpretation was a more difficult matter, and could only 
arise from considerations such as those put forward by Mr. Darwin in sup- 
port of his much-maligned theory of evolution. As he says, we have here 
a case to which no parallel was known to exist in the vegetable, or indeed 
in the animal kingdom, for in this case the individual plants “ are divided 
into two sets or bodies, which cannot be called distinct sexes, for both are 
hermaphrodites; yet they are to a certain extent sexually distinct, for 
they require reciprocal union for perfect fertility.” But the clue once 
gained, the phenomena were soon found to be not at all isolated ; and the 
researches of Mr. Darwin himself and of other observers have now brought 
to light a number of plants in which the same sort of dimorphism prevails. 
A majority of the species of Primula, certain species of Linum , several 
Pig. 2. 
Legitimate union . 
Complete fertility. 
Illegitimate 
union. 
Incomplete 
fertility. 
Long styled form. 
Short-styled form. 
