OBSERVATIONS UPON MULING AMONG PLANTS. 9 



inorganized mass ; or the pollen is scanty and white, and no de- 

 hiscence takes place. The fertility of the pollen cannot, indeed, 

 always be determined eithei' by external appearance or from 

 direct experiment, as impregnation does not always take place 

 even with pure pollen ; and some plants are more easily fecun- 

 dated with pollen taken from another individual of the same 

 species than with their own. In almost all fertile bastards, the 

 normal pollen grains are mixed with many that are smaller and 

 imperfectly organized ; and, as a general rule, the colour is less 

 vivid than in the parent species. Sufficient attention does not 

 appear at present to have been paid to the protrusion of the 

 pollen tubes in hybrids as compared with that in pure species, nor 

 to the contents of the pollen grains. 



The number of styles is also frequently increased in the 

 blossoms of hybrids, especially those which open first. It is, 

 however, far more difficult to form any judgment as to their fer- 

 tility than with respect to the stamens. Tliis may, indeed, be 

 sometimes anticipated from their preternatural elongation, the 

 far rougher surface of the stigma, or the increased time during 

 which the stigma remains moist, or in other cases by its speedy 

 discoloration. The ovules too, though often perfect externally 

 while they are really barren, are frequently shrivelled and abor- 

 tive; and even in fertile hybrids the number of ovules capable 

 of impregnation appears to be small, whatever quantity of pollen 

 be applied to the stigma. 



The greatest change in the fructifying organs takes place in 

 the union of difficious and hermaphrodite plants, affecting, how- 

 ever, as in animal hybrids, the male organs first, and to a greater 

 degree. 



We are obliged to pass without notice several chapters relative 

 to the fruitfulness of hybrids under various points of view, though 

 far from uninteresting. We proceed to consider very briefly a 

 few phenomena exhibited by the impregnation of hybrids. 



Those presented by the corolla and female organs are just 

 those which take place on the impregnation of a plant with 

 strange pollen. If the mule is tolerably fruitful, the corolla falls 

 off at the usual time; but if it is only very sparingly fertile or 

 entirely sterile, it remains longer, or the whole blossom falls. 

 The stigma continues moist long after the anthers have lost their 

 pollen, and the whole course, from the perfecting of the stigma 

 to its fading, is longer than in natural fructification. 



Even where there are a few perfect pollen grains in the 

 antiiers, impregnation does not always lake place in mules with 

 their own pollen, probably^ in consequence of the good grains 

 not'being sufficiently numerous to ensure success. Many fertile 

 mules, therefore, require artificial impregnation, and that fre- 

 quently repeated, to produce fruit : and in general typical 



