CHAP. VI. ON HETEEOSTYLED PLANTS. 251 



there is no exception to the rule that those from the 

 anthers of the short-styled form, the tubes of which 

 have to penetrate the longer pistil of the long-styled 

 form, are larger than the grains from the other form. 

 This curious relation led Delpino * (as it formerly did 

 me) to believe that the larger size of the grains in 

 the short-styled flowers is connected with the greater 

 supply of matter needed for the development of their 

 longer tubes. But the case of Linum, in which 

 the grains of the two forms are of equal size, whilst 

 the pistil of the one is about twice as long as that 

 of the other, made me from the first feel very 

 doubtful with respect to this view. My doubts have 

 since been strengthened by the class of Limnanthe- 

 mum and Coccocypselum, in which the grains are of 

 equal size in the two forms; whilst in the former 

 genus the pistil is nearly thrice and in the latter 

 twice as long as in the other form. In those species 

 in which the grains are of unequal size in the two 

 forms, there is no close relationship between the de- 

 gree of their inequality and that of their pistils. 

 Thus in Pulmonaria officinalis and in Erythroxy- 

 lum the pistil in the long-styled form is about twice 

 the length of that in the other form, whilst in the 

 former species the pollen-grains are as 100 to 78, and 

 in the latter as 100 to 93 in diameter. In the 

 two forms of Suteria the pistil differs but little in length, 

 whilst the pollen-grains are as 100 to 75 in diameter. 

 These cases seem to prove that the difference in size 

 between the grains in the two forms is not deter- 

 mined by the length of the pistil, down which the 

 tubes have to grow. That with plants in general there 

 is no close relationship between the size of the pollen- 



* 'Sull' Opera, la Distribuzione dei Sessi nelle Piante,' &c., 1867, 

 p. 17. 



