484 HEREDITY AND SEX 



Ceratopteris ihalictroides sown in soil without nitrogenous sup- 

 plies developed into male prothallia, that female organs were 

 formed when ammonium nitrate was supplied, and that wholly 

 male prothallia might become wholly female prothallia. Similar 

 results have been obtained for horsetails by Buchtien. 



It is plain, of course, that in cases like fern-prothallia and 

 Hydra, which are normally hermaphrodite, what actually occurred 

 in the experiments was the inhibition or suppression of one set of 

 sexual organs in favour of another. None the less do the experi- 

 ments suggest that the first theory is not to be dismissed too 

 hurriedly. 



Moreover, when we recall how a little nutritive attention 

 makes a worker-grub a queen-bee, or how Aphides produce 

 females parthenogenetically through months (or even years) 

 of high feeding and pleasant temperature, and how the advent 

 of autumn, with its cold and its scarcity of food, is followed by 

 a birth of males, and so on, we may not be able to share the dog- 

 matism of some who assert that the theory of the environmental 

 determination of sex is preposterous. We shall consider later 

 on the question of the influence of the environment on the 

 parents. 



§ 6. Second Theory : — That the sex is undetermined until the 

 germ-cells unite in fertilisation, when it is decided by their 

 relative condition, or by a balancing of the tendencies they 

 bear, neither sperm nor ovum being necessarily decisive 



It has been a favourite theory, especially in regard to man 

 and mammals, that the sex of the offspring depends upon the 

 relative condition of the germ-cells at fertilisation, the differences 

 in condition depending on the relative age of the parents and 

 other such circumstances. Let us consider various forms of 

 this second theory. 



Hofacker (1828) and Sadler (1830) independently published 



