410 Origin of Each Species Considered Separately. 



pollen as I could on the stigmas of a few flowers ; but 

 all to no purpose. Then, as it was difficult to liberate 

 the pollen direct from the anthers on to the stigma, I 

 teased it out with needles on to a glass slide, collected 

 it in a lump and transferred it direct from this to the 

 stigma — but, again, all to no purpose. 



After this I pollinated the flowers, without castrating 

 them, with the pollen of a remotely related plant, be- 

 longing in fact to another subgenus; O. odorata.^ I 

 have obtained fertile crosses between this form and 0. 

 Lamarckiana, O. biennis and O. miiricata. It ought, 

 then, to be able to fertilize O. lata also; but my attempts 

 to effect this were practically without result although 

 I pollinated many flowers on four plants. Only a single 

 seed germinated ; and this produced a hybrid plant. This 

 experiment also shows that self-fertilization did not 

 occur. 



Besides this I have pollinated castrated and non- 

 castrated flowers of O. lata with the pollen of O. La- 

 marckiana. I have also tried the effect of putting very 

 little Laniarckiana-poWcn on the stigmas of uncastrated 

 flowers in the hope that perhaps I might induce self- 

 fertilization in that way. All these experiments gave 

 exactly the same result; about 15-20% of the seeds gave 

 O. lata, the rest 0. Lamarckiana. 



I conclude from these and from a number of other 

 experiments that the pollen of O. lata, in spite of the 

 presence of occasional apparently good grains, is never- 

 theless absolutely sterile. One result of the establishment 

 of this fact is that the castration of flowers of 0. lata in 

 hybridization experiments becomes unnecessary. 



^ From the subgenus Oenothera (Euoenothera) ; whilst O. La- 

 marckiana etc. belong to the subgenus Onagra. 



