II.] HETEROMORPHOUS FLOWERS. 39 



in Hottonia, and shrewdly observed that there was 

 probably some reason for it, but was unable to 

 suggest any explanation. 



In Lythrum the existence of different forms had 

 been observed by Vaucher in 1841, and in the genus 

 Oxalis by Jacquin, who regarded them as indicative 

 of different species ; but it was reserved for the genius 

 and perseverance of Mr. Darwin to explain (" Jour. 

 Linn. Soc." 1862, p. 77) the significance of this curious 

 phenomenon, and the important part it plays in the 

 economy of the flower. Now that Mr. Darwin has 

 pointed this out, it is sufficiently obvious : An insect 

 thrusting its proboscis down a primrose of the long- 

 styled form (Fig. 38) would dust its proboscis at a 

 part which, when it visited a short-styled flower 

 (Fig. 39), would come just opposite the head of the 

 pistil, and could not fail to deposit some of the 

 pollen on the stigma. Conversely, an insect visiting 

 a short-styled plant, would dust its proboscis at a 

 part further from the tip ; which, when the insect sub- 

 sequently visited a long-styled flower, would again 

 come just opposite to the head of the pistil. Hence 

 we see that by this beautiful arrangement, insects 

 must carry the pollen of the long-styled form to the 

 short-styled, and vice versd. 



There are other points in which the two forms differ 

 from one another ; for instance, the stigma of the long- 

 styled form is globular and rough, while that of the 

 short-styled is smoother, and somewhat depressed. 

 The pollen of the two forms (Figs. 38 and 39) is 

 also dissimilar ; that of the long-styled being con- 

 siderably smaller than the other TQ^ of an inch in 



