•310 TUB JOURNAL OF BOTANY 



THE POLLINATION OP THE PRIMROSE. 

 Br A. A. Dalluan, P.C.S. 



Although heterostylism is now so familiar a feature in certain 

 species, it does not appear — at least, so far as the genus Primula is 

 concerned — to have been noticed by tbe older botanists. It was not 

 until the close of the eighteenth century that William Curtis (PI. 

 Lond. fasc. vi. t. 1G) mentioned the two flower forms in Primula 

 acaulis L. (P. vulgaris Huds.), and this appears to be the earliest 

 reference to heterostyly in the Primrose. Some seventy years later 

 the subject engaged the attention of Charles Darwin, who, on 

 November 21st, 1861, read before the Linnean Society a paper " On 

 the Two Forms, or Dimorphic Condition, in the Species of Primula 

 and on their remarkable Sexual Relations" (Journ. Linn. Soc. (JBot.) 

 vi. 77) ; in this four species — P. vulgaris Huds., P. verts L., 

 P. si)iensis Sabine, and P. Auricula L. — received special notice. 

 The morphological and anatomical differences subsisting between the 

 two forms of flower in each species are dealt with and considered in 

 conjunction with the experimental results from different types of 

 cross-pollination. Darwin emphasises these facts, and shows that the 

 occurrence of floral dimorphism in Primula must be regarded as 

 a device " to favour the intercrossing of distinct individuals." This 

 formed the foundation of his further work on heterostyly, which was 

 brought together in 1877 in his book entitled Different Forms of 

 Flowers on Plants of the same Species. 



The mode of pollination of the Primrose — and to a less extent of 

 the Cowslip — has long been a matter of doubt. Darwin himself 

 was conscious of this difficulty: in his paper he states (p. 85): — 

 " I have watched Primroses more attentively during several years, 

 and have never seen an insect visit them ; yet from their close simi- 

 larity in all essential respects to Cowslips, there can hardly be a doubt 

 that they require the visits of insects. Hence 1 am led to suppose 

 that both Primroses and Cowslips are visited by moths." Later 

 (Forms of Flowers, p. 56) he writes : — " The Primrose is never 

 visited (and I speak after many years' observation) by the larger 

 humble-bees and rarely by the smaller kinds ; hence its fertilisation 

 must depend almost exclusively on moths." A careful perusal of 

 Darwin's various writings on the subject shows that he considered 

 the pollination of the Primrose was mainly accomplished by nocturnal 

 Lepidoptera, and to some slight extent by Thrips. It should be 

 observed, however, that this was merely a supposition, for neither he 

 nor later writers have actually seen moths visiting the Primrose. 

 Various subsequent writers have, however, stated it as a fact : thus 

 Lord Avebury says of the Primrose (Life History Brit. Fl. PL 269: 

 1 9Q5) . — " It appears to be mainly fertilised by moths." 



Although a number of visitors are on record for the Primrose, 

 yet careful investigation of the evidence adduced indicates its insuffi- 

 ciency. In this connection Mr. Burkill (Journ. Bot. 1897, 186) 

 writes : — " The fertilization of this plant is still unexplained. None 

 of the insects seen on it through many hours of Avatching are suffi- 

 cient for its fertilization The doubt does not end with our 



