stout: pollinations in CICHORIUM INTYBUS 335 



to various sorts of sterility, especially as it appears in animals. 

 Here belong such cases as: 



(a) Complete impotence involving either the absence of all 

 floral and sex organs as in Pelargonium Madame Salleron or the 

 lack of sporophylls only as in certain double-flowered plants like 

 Matthiola: 



(b) Partial or complete impotence with reference to one or the 

 other type of sporophyll as seen in such cases as impotence of 

 pistils only in double-flowered varieties of Petunia; in the impo- 

 tence of stamens as in Oenothera lata; in the marked impotence of 

 both sporophylls (failure to develop normal spores), as in the well- 

 known cases of contabescence of anthers and impotence of pistils 

 with abnormal development of spores, as exhibited by many 

 hybrids and by such plants as Oenothera Lamarckiana whose 

 hybrid origin is at least more remote; in the marked impotence of 

 parthenocarpic varieties, as in Citrus species; in the impotence of 

 the male sex organs as in the grape; or that of the female sex 

 organs, as in red clov^er (arrested sexual differentiation) at certain 

 stages. 



While the causes are no doubt physiological, impotence ex- 

 presses itself as a failure in the development of the reproductive 

 organs or of the germ cells themselves, rather than as a failure in 

 the proper functioning in fertilization of such organs or germ cells. 

 They are all essentially cases of degeneration in the sporophyte, 

 including the production of its spores, excepting the cases of 

 degeneration of a maturing gametophyte itself, such as Dorsey 

 ('14) has described in Vitis. 



Impotency of certain types may be either temporary or perma- 

 nent, both in animals and in plants, and may exhibit variations and 

 fluctuations especially in response to such factors as disease and 

 cultural conditions. 



II. Sterility from incompatibility. — This class includes plants 

 which produce apparently normal reproductive organs and germ 

 cells, but which are nevertheless sterile through either a structural 

 or a functional incompatibility. The old question whether there 

 can be a functional failure without a structural cause I shall not 

 discuss here. 



The term incompatibility has been, of course, used to charac- 

 terize a wide range of causes of failure in reproduction, but it can 



