WHAT EVOLUTION IS n 



The explanation offered by La- 

 marck turned chiefly on the effect 

 upon organisms of the surroundings 

 or environment. Lamarck noted that 

 marsh plants, such as the aquatic 

 Ranunculus, which grew partly sub- 

 merged and partly out of water, had 

 leaves of different shapes in the two 

 situations. Under water the leaves 

 were finely divided, but in the air they 

 were simply lobed. This difference 

 he rightly conceived to be due to the 

 environment, one situation producing 

 the first type of leaf and the other the 

 second. He looked upon this as a 

 direct effect of the surroundings and 

 regarded it of great importance par- 

 ticularly with plants. A special plant 

 being thus directly dependent upon its 

 surroundings for its peculiar form, any 

 change in these surroundings would 

 be likely to be followed by a change 

 in the form of the plant, that is, an- 



