SEXUALITY AND THE ENVIRONMENT. 243 



petaloid forming staminodia — another hint that " conta- 

 bescence " is closely akin to petalody of the androecium. 



Sexuality and Heterogamy. — Another source of diclinism 

 may theoretically be attributed to protandry and protogyny 

 carried to such a degree that the opposite sex is arrested 

 altogether. Many plants have their flowers hovering about 

 homogamy, some individuals being protandrous, others proto- 

 gynous, according to locality, etc. Thus Saxifrages and 

 species of Ribes are in this condition. 



We know that as soon as a flower is fertilised, the corolla 

 fades and mostly falls. This means that the nourishment is 

 now directed into the pistil. In a protogynous flower the 

 petals and stamens may be in a very undeveloped state, while 

 the stigma is ready for pollination.* If it be fertilised it 

 no longer requires other organs, and nourishment may be 

 absti-acted from the corolla and stamens, which therefore 

 would tend to abort. Let this procedure become hereditary, 

 and we get passages to female flowers. Moreover, the more 

 female forms tend less to degeneracy, plant for plant, than 

 the hermaphrodites, as Darwin showed with Satureia, and as 

 is known to be the case with Strawberries in the United 

 States, and again as is the case with the Ash, described above. 

 Therefore female plants might be produced abundantly which 

 would keep that form permanent. 



Conversely, plants growing in the open with an increase 

 of temperature, and readily seen and visited by insects, 

 become strongly protandrous ; consequently the pistil is at 

 first delayed in development wdth a corresponding tendency 

 to enfeeblement in comparison with the more purely female 

 plants. 



The results of crossing these conspicuous flowers — and 



* See e.g. Miiller's figures of Saxifraga Seguieri in different stages, 

 Fertilisation, etc., p. 244. 



