90 HETEKOSTYLBD DIMOKPHIC PLANTS. Chap. III. 



stigmatic tissue deeply, and the stigmas themselves 

 do not soon become discoloured and twisted. 



This seems to me a remarkable physiological fact. 

 The pollen-grains of the two forms are undistinguish- 

 able under the microscope ; the stigmas differ only in 

 length, degree of divergence, and in the size, shade of 

 colour, and approximation of their papillae, these latter 

 differences being variable and apparently due merely 

 to the degree of elongation of the stigma. Yet we 

 plainly see that the two kinds of pollen and the two 

 stigmas are widely dissimilar in their mutual reaction 

 — the stigmas of each form being almost powerless on 

 their own pollen, but causing, through some myste- 

 rious influence, apparently by simple contact (for I 

 could detect no viscid secretion), the pollen-grains of 

 the opposite form to protrude their tubes. It may be 

 said that the two pollens and the two stigmas mutually 

 recognise each other by some means. Taking fertility 

 as the criterion of distinctness, it is no exaggeration to 

 say that the pollen of the long-styled Linum grandi- 

 florum (and conversely that of the other form) has been 

 brought to a degree of differentiation, with respect to 

 its action on the stigma of the same form, correspond- 

 ing with that existing between the pollen and stigma 

 of species belonging to distinct genera. 



Linum perenne. — This species is conspicuously hetero- 

 styled, as has been noticed by several authors. The 

 pistil in the long-styled form is nearly twice as long as 

 that of the short-styled. In the latter the stigmas are 

 smaller and, diverging to a greater degree, pass out 

 low down between the filaments. I could detect no 

 difference in the two forms in the size of the stigmatic 

 papillae. In the long-styled form alone the stigmatic 

 surfaces of the mature pistils twist round, so as to face 

 the circumference of the flower ; but to this point 1 



