250 CONCLUDING EEMAEKS Chap. VL 



anthers of the short-styled form, the tuhes 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 cases 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 tD 

 75 in diameter. These cases seem to prove that the 

 difference in size between the grains in the two 

 forms is not determined by the length of the pistil, 

 down which the tubes have to grow. That with 

 plants in general there is no close relationship between 



* ' Suir opera, la Distribuzione dei Seasi uelle Piunte,' &c., 1867, 

 p. 17. 



