230 THE STRUCTURE OF FLOWERS 



or by the brooks in tlie neighbourhood of this fair city. It is 

 especially interesting as the flower which first led Sprengel to his 

 researches. " In the year 1787," writes Sir John Lubbock, " he 

 (Sprengel) observed that in the corolla of this species there are a 

 number of delicate hairs, and convinced, as he says, 'that the wise 

 Author of Nature would not have created a single hair in vain,' 

 he endeavoured to ascertain the use of these hairs and satisfied 

 himself that they served to protect the honey from rain." Another 

 point of interest in this flower is the spontaneous movement of 

 the stamens and pistils. Kolreuter seems to have been the first to 

 observe this motion in another dichogamous plant, Ruta graveolens. 

 He supposed that the object was to bring the stamen in contact 

 with the pistil and so insure close fertilisation. Nature, as 

 Sprengel pointed out, had a very difl'erent purpose to fulfil. It was 

 to bring the stamen and pistil successively in contact with the 

 same part of the insect's body, and so insure cross-fertilisation. 

 When the flower first opens, the stamens lie on the petals, at right 

 angles with the upright pistils. As they come to maturity they 

 raise themselves parallel, and close to the pistil, which is, however, 

 not yet capable of fertilisation. After they have shed their pollen 

 they return to their original position and the stigmas unfurl them- 

 selves. As the stigmas do not become mature until all the stamens 

 have shed their pollen, G.pratcnse is wholly dependent upon insect 

 aid for fertilisation. The spontaneous movement thus ensures 

 cross-fertilisation, and indicates another of Nature's plans for 

 bringing about the end desired by making certain insects the 

 carriers of the pollen. 



I will now direct attention to another very successful arrange- 

 ment for promoting cross-fertilisation through the agency of insects. 

 Probably many have noticed the Primroses {Primula vulgaris^ 

 Fig. 4) i)resent different appearances with regard to the stamens 

 and pistils. In some the pistil is ibund at the top of the tube, 

 and the stamens half way down ; in others the stamens are at the 

 top of the tube, and the pistil half way down. Corresponding 

 differences may be seen in the Cowslip {T. veris), Polyanthus, 

 and Auricula. This difference in the form of the flowers has 

 long been known by the homely names of " thrum-eyed and pin- 

 eyed." Plants which present these differences of form are known 



