276 THE STRUCTURE OF FLOWERS. 



plant. The affection cannot be cured by any change of 

 treatment, and is propagated by layers, cuttings, etc., and 

 perhaps even by seed. In contabescent plants the female 

 organs are seldom aifected, or merely become precocious in 

 their development. The cause of this affection is doubtful, 

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

 plants of Dianthus and Verhascum 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 

 occurrence 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 abound. 

 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 

 very frequently induced by inclement weather. He mentions 

 * A like cause produces petalody of stamens, see p. 299. 



