CLEISTOGAMOUS FLOWERS. 



[CHAP. 



Elthamensis," vol. ii. p. 239). As, however, they have no 

 relation to our present subject, I shall not now dwell 

 upon them. 



I pass on, therefore, to the genus Primula. If a 

 number of specimens of primroses or of cowslips be 

 examined, we shall find that about half of them 

 have the pistil at the top of the tube, and the 

 stamens half-way down (as is shown in Fig. 38), 

 while the other half have, on the contrary, the 

 stamens at the top of the tube, and the pistil half- 

 way down (as shown in Fig. 39). Corresponding 



CO 



X 250 



FIG. 38. Primula (long-styled form). FIG. 39. Primula (short-styled form). 



differences occur in Polyanthus and Auricula, and 

 have long been known to gardeners, and even to 

 schoolchildren, by whom the two forms are distin- 

 guished as " thrum-eyed " and " pin-eyed." As 

 already mentioned, plants which present these differ- 

 ences are known as Heteromorphous (in opposition to 

 those which are Homomorphous^ or have only one 

 kind of flower), while those with two forms are called 

 Dimorphous, those with three, Trimorphous. 



Sprengel himself had noticed a case of Dimorphism 



