CHAP. VL ON HETEROSTYLED PLANTS. 247 



the corolla, and in Pontederia in its colour. In the re- 

 productive organs the differences are much greater and 

 more important. In the one form the stamens may be 

 all of the same length, and in the other graduated in 

 length, or alternately longer and shorter. The fila- 

 ments may differ in colour and thickness, and are 

 sometimes nearly thrice as long in the one form as in the 

 other. They adhere also for very different proportional 

 lengths to the corolla. The anthers sometimes differ 

 much in size in the two forms. Owing to the rotation 

 of the filaments, the anthers, when mature, dehisce to- 

 wards the circumference of the flower in one form of 

 Faramea, and towards the centre in the other form. The 

 pollen-grains sometimes differ conspicuously in colour, 

 and often to an extraordinary degree in diameter. 

 They differ also somewhat in shape, and apparently in 

 their contents, as they are unequally opaque. In the 

 short-styled form of Faramea the pollen-grains are 

 covered with sharp points, so as to cohere readily to- 

 gether or to an insect ; whilst the smaller grains of the 

 long-styled form are quite smooth. 



With respect to the pistil, the style may be almost 

 thrice as long in the one form as in the other. In 

 Oxalis it sometimes differs in hairiness in the three 

 forms. In Linum the pistils either diverge and pass 

 out between the filaments, or stand nearly upright and 

 parallel to them. The stigmas in the two forms often 

 differ much in size and shape, and more especially in 

 the length and thickness of their papillae; so that 

 the surface may be rough or quite smooth. Owing to 

 the rotation of the styles, the papillose surface of 

 the stigma is turned outwards in one form of Linum 

 perenne, and inwards in the other form. In flowers of 

 the same age of Primula veris the ovules are larger in 

 the long-styled than in the short-styled form. The 



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