SEXUALITY AND THE ENVIKONMENT. 241 



30-35 mm. diameter. In both these extreme forms the outer 

 row of florets possesses greatly enlarged radiating corollas 

 which are sexually functionless, but useful in making the 

 flower-mass more conspicuous. ^ In the male flower-heads, 

 anthers and pistils of the disk-florets are well-developed, 

 but the style-branches never open so as to expose their 

 stigmatic surfaces, and in their basal portion are grown 

 together. In the female flower-heads, on the contrary, only 

 the pistil of the disk-florets is fully developed, the anthers 

 being pollenless, shrivelled, and brownish coloured 



" These two extreme forms are linked with the original 

 one by a continuous series of gradations When in the 

 orio-inal form variation begins in one direction, the outer 

 i-ow of florets gradually becomes longer and more radiating, 

 and in the same degree their sexual organs diminish in size 

 and become functionless, the anthers first aborting, and then 

 the pistil. Finally, the barren ray-florets continuing to 

 increase, the pistils of the disk-florets, too, become function- 

 less, and the conspicuous male flower-head is accomplished. . 



" In the contrary variation some of the outer florets of 

 the oriodnal form besrin to diminish in size, while their 

 anthers become brownish and pollenless, and this change 

 step by step proceeds inwards and seizes a greater and 

 greater number of disk-florets, until the whole flower-head 

 is female, and reduced to a diameter of 15-18 mm. This 

 state bemg reached, the corollas of the marginal flowers 

 recommence to increase and become radiating, while at 

 the same time their anthers disappear without leaving any 

 trace, and their style-branches remain closed together." 



Calendula officinalis furnishes another instance of com- 

 plete change of sex, most probably caused by varying con- 

 ditions of nutrition supplied by the soil. In the normal 

 " single " form the disk florets are male, but with club- 



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