Ghap. IV. PONTBDBRIA. 183 



stands on a level with the upper ones of the short-styled 

 form. In the latter the stigma is seated beneath both 

 its own sets of anthers, and is on a level with the an- 

 thers of the shorter stamens in the long-styled form. 

 The anthers of the longer stamens of the short-styled 

 form are to those of the shorter stamens of the long- 

 styled form as 100 to 88 in length. The pollen-grains 

 distended with water from the longer stamens of the 

 short-styled form are to those from the shorter stamens 

 of the same form as 100 to' 87 in diameter, as deduced 

 from ten measurements of each. kind. We thus see that 

 tlje organs in these two forms differ from one another 

 and are arranged in an analogous manner, as in the 

 long- and short-styled forms of the trimorphic species 

 of Lythrum and Oxalis. Moreover the longer stamens 

 of the long-styled form of Pontederia, and the shorter 

 ones of the short-styled form, are placed in a proper 

 position for fertilising the stigma of a mid-styled form. 

 But Fritz Miiller, although he examined a vast number 

 of plants, could never find one belonging to the mid- 

 styled form. The older flowers of the long-styled 

 and short-styled plants had set plenty of apparently 

 good fruit; and this might have been expected, as 

 they could legitimately fertilise one another. Al- 

 though he could not find the mid-styled form of 

 this species, he possessed plants of another species 

 growing in his garden, and all these were mid-styled; 

 and in this case the pollen-grains from the anthers of 

 the longer stamens were to those from the shorter sta- 

 mens of the same flower as 100 to 86 in diameter, as 

 deduced from ten measurements of each kind. These 

 mid-styled plants growing by themselves never pro:- 

 duced a single fruit. 



Considering these several facts, there can hardly 

 be a doubt that both these species of Pontederia are 

 14 



