814 THE EFFECTS OF CONDITIONS 



G. A. Brennan * records that he set out this plant in 

 1872, giving it very rich treatment. " In 1874 it be- 

 gan to deviate from the original trimerous type and to 

 assume the tetramerous one, by developing another 

 petal, and instead of doing this at the expense of the 

 pistil or stamens, it added another sepal, another carpel 

 with style, and two stamens, thus making a typically 

 tetramerous flower." In 1876 a pentamerous plant was 

 evolved; in 1879 a hexamerous; in 1882 a dimerous; 

 and in 1884 a heptamerous. Thus as the result of thir- 

 teen years of cultivation, "a monocotyledonous plant 

 has in bloom, at the same time, flowers of dimerous, 

 trimerous, tetramerous, pentamerous, hexamerous, and 

 heptamerous types respectively, each flower having 

 twice as many stamens as sepals, petals, or carpels of 



ovarv.' 



To turn to the Animal Kingdom, an interesting in- 

 stance of variation following directly on change of en- 

 vironment is that noticed by Costa t in the oyster. 

 Thus, on transferring young oysters from English shores 

 to the Mediterranean, it was found that their manner 

 of growth at once altered, and prominent diverging rays 

 were formed, like those on the shells of the native 

 Mediterranean oyster. The variations noticed by Ley- 

 dig J in the snail Helix nemoralis are attributed by him 

 to the direct influence of environment, and this may be 

 actually the case, but there is no evidence to prove it. 

 He noticed that at Mainz the shell of this snail exhibits a 

 fine citron yellow. This hue disappears further down the 



*Amer. Naturalist, vol. xx. 551, 1886. 



f Quoted from " Animals and Plants," ii. p. 270. 



\ Eimer's " Organic Evolution," p. 137. 



