Origin of Peloric Toadflax 471 



tation, it seems worth while to give some details 

 regarding their fertilization. 



Isolated plants of Linaria vulgaris do not 

 produce seed, even if freely pollinated by bees. 

 Pollen from other plants is required. This re- 

 quirement is not at all restricted to the genus 

 Linaria, as many instances are known to occur 

 in different families. It is generally assumed 

 that the pollen of any other individual of the 

 same species is capable of producing fertiliza- 

 tion. Although it is to be said that a critical 

 examination has been made in but few instances. 



This, however, is not the case, at least not in 

 the present instance. I have pollinated a num- 

 ber of plants, grown from seed of the same 

 strain and combined them in pairs, and ex- 

 cluded the visits of insects, and pollen other 

 than that of the plant itself and that of the spec- 

 imen with which it was paired. The result was 

 that some pairs were fertile and others barren. 

 Counting these two groups of pairs, I found 

 them nearly equal in number, indicating there- 

 by that for any given individual the pollen of 

 half of the others is potent, but that of the other 

 half impotent. From these facts we may con- 

 clude the presence of a curious case of dimor- 

 phy, analogous to that proposed for the prim- 

 roses, but without visible differentiating marks 

 in the flowers. At least such opposite charac- 



