DEGENEKACY OF FLOWERS. 277 



the case of " Ononis, growing and flowering abundantly on 

 the ' Sand-totts ' near Burnliam, on the Bristol Channel, in 

 which plant scarcely a grain of normal form was to be 

 found ; many were absolutely united into grotesque groups 

 and utterly deformed. At the commencement of the cold 

 weather of autumn, although the corolla may appear unin- 

 jured, the pollen grains are often 'dirty,' unable, as it were, 

 to throw off the residual tissue surrounding them, and are 

 often irregularly reduced in size." 



This sensitiveness of pollen .to barren soil, inclement 

 weather, etc., at once throws light on a probable origin of 

 diclinisra, such as of gy no-dioeceous plants already mentioned; 

 and simply confirms the idea that these differences in the 

 sexual systems of plants must not be looked upon as so many 

 beneficial arrangements, but simply inevitable results which 

 must follow such circumstances as give rise to them, whether 

 they may prove advantageous or not. The injurious effect 

 of over-crossing, abundantly proved by florists, Mr. White 

 recognizes in the character of the grains of Rhododendrons 

 and Ericas, which exhibit a shrivelling up and occasionally 

 a complete " dissolution " of one and the uppermost grain of 

 the group of four. And this observer adds, that in more 

 than one species of Erica and also of Vaccinium the injury, 

 he thinks, has become chronic. 



If the " vegetative " system be too energetic the " repro- 

 ductive" is sure to suffer, and one of the primary causes of 

 the injury is the arrested state of the pollen, as Van Tieghem 

 has described and figured it in Hanunculus Ficaria.* A 

 like result occurs in many cultivated plants, as Mr. Darwin 

 has pointed out when describing the " contabescence of 

 anthers." % 



*See above, p. 231, note. 



t An. and PI. uncler Dom., vol. ii., p. 165. 



