276 THE STBUCTURE OF FLOWEES. 



plant. The affection cannot be cared by any change of 

 treatment, and is pi-opagated by layers, cuttings, etc., and 

 perhaps evea by seed. In contabescent plants the female 

 organs are seldom affected, or merely become precocions in 

 their development. The canse of this affection is donbtful, 

 and is different in different cases. . . . The contabescent 

 plants of Bianfhus and Verbascitm found wild by Wiegmann 

 grew on a dry and sterile bank." * 



" Cases of an opposite nature likewise occur — namely, 

 plants with the female organs struck with sterility, whilst 

 the male organs remain perfect." 



The constancy or prevalence of this condition of conta- 

 bescence seems to be the first indication of diclinism, what- 

 ever the cause ; and Silene inflata may be mentioned as 

 frequently furnishing good examples of both kinds of 

 contabescence. 



Degeneracy of the Pollen. — As this is a feature of 

 importance in the general degradation of flowers, a few 

 words may be added in reference to it. It is of frequent 

 occnn-ence in cultivated plants ; thus Potatoes are notorious 

 for failing to produce fruit ; and some varieties are much less 

 liable to do so than others, Mr. C. F, White, F.L.S., tells 

 me he regards this plant as furnishing the most conspicuous 

 example of a form of degradation of pollen ; the pollen 

 grains of a normal character are very generally not to be 

 found at all, but round, square, and polygonal forms abonnd. 

 On the other hand, he gathered many flowers, in a large 

 field in the Isle of Thanet, with scarcely a grain imperfect 

 in shape or reduced in size. 



Mr. White has noticed, in his numerous researches 

 among pollens, that degeneracy by dwarfing is mostly or 

 veiy frequently induced by inclement weather. He mentions 

 • A like cause prodnoea petalody of Btamens, see p. 299. 



