THE HIGHER DICOTYLEDONS. 343 



" This object would also be effected by the visits of Andrena 

 gwynana, but this insect must be placed in a different category from 

 the bee, for it is a regular and busy visitor of the Primrose and more 

 often seen by me on its flowers than on those of other plants. It was 

 only observed towards the close of my visit when the weather was 

 much milder, but then it was present in considerable numbers. It 

 gathered the pollen greedily and in getting at it poked its head deep 

 into the mouth of the corolla. 



"From the instances given above, therefore, there is no doubt in my 

 mind that Primroses are efficiently cross-pollinated in the district 

 under observation by Bombylius, Anthophora, and Andrena, with the 

 addition of occasional though by no means isolated visits of Bombus. 



" That self-pollination may occur fairly often in the Primrose cannot 

 be denied, and, indeed, Darwin observed the frequent occurrence in 

 both Cowslip and Primrose of Thrips, which he considered aided the 

 self -fertilisation of both forms. In many Primroses which I examined 

 numbers of Thrips were present, and in these flowers it was very com- 

 mon to find pollen-grains scattered throughout the tube of the corolla 

 and it seemed likely that it had been carried about there by these 

 small insects. Another agency for self-pollination is no doubt the 

 wind, taken in conjunction with alterations in the position of the 

 flower. 



"In the absence of cross-pollination, which must frequently fail in 

 flowering plants in early spring, the strong winds of that season are 

 probably of considerable use. In the Primrose the flowers open at 

 first in a vertical position, and if the flower is short-styled the pollen 

 from the opening anthers can readily be shaken by the wind on to the 

 lower-standing stigma. But towards the end of flowering the flower- 

 stalk has grown considerably in length and the flower passes into a 

 horizontal and often a pendant position, so that the long- styled forms 

 have a chance of self-pollination too when the flowers are agitated by 

 the wind. 



"It may be thought that this movement is mainly for the concealment 

 of the fruits, which in the Primrose are ripened beneath the foliage, but 

 though this may be to a certain extent the case, I cannot but believe 

 that the self-pollination is also a determining factor in this movement. 

 For in the Cowslip the very opposite occurs. The flowers, at first 

 pendant, offer greater facilities as far as self-pollination is concerned to 

 the long-styled forms, but later on the flowers become erect and thus 

 in the absence of cross-pollination the short-styled forms will have 

 ample opportunity to be self -pollinated. 



"From the observations I have made on the Primrose I feel con- 

 vinced that it is both regularly visited and cross -pollinated by insects 

 under favourable climatic conditions, but that like most flowers adapted 

 to the visits of insects it is provided with efficient means for self-pol- 

 lination, and these are important to a plant flowering at so early a 

 period of the year, when the visits of insects may be precarious. " 



Watch insects visiting the flowers of Primrose and Cowslip : 

 in the former case the flat top of the erect corolla serves as a 



