16 HETEROSTYLED DIMORPHIC PLANTS. CHAP. L 



is globular; in the short-styled it is depressed on 

 the summit, so that the longitudinal axis of the 

 former is sometimes nearly double that of the latter. 

 Although somewhat variable in shape, one difference 

 is persistent, namely, in roughness: in some speci- 

 mens carefully compared, the papillae which render 

 the stigma rough were in the long-styled form from 

 twice to thrice as long as in the short-styled. The 

 anthers do not differ in size in the two forms, which 

 I mention because this is the case with some hetero- 

 styled plants. The most remarkable difference is in 

 the pollen-grains. I measured with the micrometer 

 many specimens, both dry and wet, taken from plants 

 growing in different situations, and always found a 

 palpable difference. The grains distended with water 

 from the short-styled flowers were about -038 mm. 

 (-y^Q- of an inch) in diameter, whilst those from the 

 long-styled were about 0254 mm. ( 7 Q of an inch), 

 which is in the ratio of 100 to 67. The pollen-grains 

 therefore from the longer stamens of the short-styled 

 form are plainly larger than those from the shorter 

 stamens of the long-styled. When examined dry, 

 the smaller grains are seen under a low power to 

 be more transparent than the larger grains, and 

 apparently in a greater degree than can be ac- 

 counted for by their less diameter. There is also a 

 difference in shape, the grains from the short-styled 

 plants being nearly spherical, those from the long- 

 styled being oblong with the angles rounded; this 

 difference disappears when the grains are distended 

 with water. The long-styled plants generally tend 

 to flower a little before the short-styled : for instance, 

 I had twelve plants of each form growing in separate 

 pots &nd treated in every respect alike; and at the 

 time when only a single short-styled plant was' in 



