EVOLUTION OF PLANTS, AND DIRECTIVITY OF LIFE. 343 



crowfoot. The submerged leaves are divided up into thread-like 

 segments. This is the result of response to the water, but if the seed 

 be sown in a garden the plants grow to maturity, retaining the aquatic 

 form, but adopting the anatomical structure for an aerial existence. 



The preceding are but a few typical illustrations of response to 

 changed conditions of life. It is not too much to say that every 

 structure, every cell, is really formed with its own definite purpose, 

 carried out by the act of response, under the Directivity of Life. 



The blades can become degenerate, as in leaf-scales on underground 

 stems, but are useful in bulbs, as storage-organs. 



Similarly, they are more or less useless as small bracts, but can 

 acquire uses, as when they are brightly coloured or are subfoliaceous. 

 But we are here passing on to the reproductive organs, which will be 

 the subject of the next lecture. 



