21 
Here then we have a short-styled variety on the left, the 
anthers reaching some height above the stigma; it is easy 
enough to imagine how the pollen may drop from these an- 
thers on the stigma and so fertilize it. But what about this 
long-styled pin centre on the right, where the stigma stands 
above the pollen bearing organs, and so does not stand any 
chance of being fertilized? Now the first thought that struck 
Mr. Darwin was this, that the Primrose was gradually becoming 
diecious, i.e. that by and by the stamens would die out in the 
long-styled specimens, and the plant would bear only a pistil ; 
and that in the short styled specimens the pistil was dying out 
and the stamens were developing themselves. It is the case 
in many plants that some flowers bear pistils only and others 
stamens only—they are called dzecious or ‘‘ /wo-housed.” 
Thus in time we should get two sorts of primroses much 
more distinct than they are at present. Again, the thought 
may strike you at once, that if the pollen cannot reach the 
stigma on the long-styled specimens there can be no fertili- 
zation, and therefore no seed, and consequently the pin 
centres must in time die out. Now we must ask some bo- 
tanical friend whether he knows for a certainty that the pin 
centres ever pro‘luce seed. He says ‘‘ Yes, quite as often as 
the others.” ‘lherefore they do get fertilized. This sets us 
thinking again—how? Mr. Darwin says it is done by the 
Humble Bee. Many of you will recollect how by the agency 
of this and other insects orchids are fertilized. The bee 
inserting its head into the corolla of a flower detaches some 
of the pollen, and upon entering another is pretty certain to 
leave some of it behind. It is now a well-known fact that 
this process, which is called cross-fertilisation, is the rule and 
not the exception; the exceptions lie on the other side, the 
case of a flower fertilizing itself by its own pollen, being rare 
even in flowers like the short-styled primroses. And when 
such self-fertilization takes places the seed deteriorates. 
But then you will say in a case like this—the short-styled 
Primrose—how is it possible to prevent self-fertilization ? 
Now we make use of another or two of Mr. Darwin’s discove- 
ries in the physiology of plants. He discovered that when a 
stigma is covered with two or three kinds of pollen,—species 
or varieties, one only takes effect to the exclusion of all others; 
also that the polle1. from a long-styled Primrose is more 
