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 

 dicEcious, 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 dimcious or " /z£;(9-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 proiluce seed. He says " Yes, quite as often as 

 the others." Therefore 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 tw j or three kinds of pollen, — species 

 or varieties, one only takes eff"ect to the exclusion of all others; 

 also that the pollei. from a long-styled Primrose is more 



