Chap. I. PRIMULA VERIS. 23 



dead humble-bee, or a thick bristle or rough needle, 

 be pushed down the corolla, first of one form and 

 then of the other, as an insect would do in visiting the 

 two forms growing mingled together, pollen from 

 the long-stamened form adheres round the base of 

 the object, and is left with certainty on the stigma 

 of the long-styled form; whilst pollen from the short 

 stamens of the long-styled form adheres a little way 

 above the extremity of the object, and some is 

 generally left on the stigma of the other form. In 

 accordance with this observation I found that the 

 two kinds of pollen, which could easily be recog- 

 nised under the microscope, adhered in this manner 

 to the proboscides of the two species of humble- 

 bees and of the moth, which were caught visiting 

 the flowers; but some small grains were mingled 

 with the larger grains round the base of the proboscis, 

 and conversely some large grains with the small 

 grains near the extremity of the proboscis. Thus 

 pollen will be regularly carried from the one form 

 to the other, and they will reciprocally fertilise one 

 another. Nevertheless an insect in withdrawing its 

 proboscis from the corolla of the long-styled form 

 cannot fail occasionally to leave pollen from the same 

 flower on the stigma; and in this case there might 

 be self-fertilisation. But this will be much more 

 likely to occur with the short-styled form; for when I 

 inserted a bristle, or other such objects in the corolla 

 of this form, and had, therefore, to pass it down be- 

 tween the anthers seated round the mouth of the 

 corolla, some pollen was almost invariably carried 

 down and left on the stigma. Minute insects, such 

 as Thrips, which sometimes haunt the flowers, would 

 likewise be apt to cause the self -fertilisation of both 



forms. 



4 



