THE FLOWER 223 



science, and has greatly enlarged our knowledge of the life 

 history of both plants and animals, by bringing to light re- 

 semblances that exist between the most widely divergent 

 species in their earlier stages of development and thus 

 showing traces of a common origin. It has shown further, 

 that every individual plant or animal, in its development 

 from the embryo to the mature state, passes briefly through 

 stages apparently similar to those which the species has trav- 

 ersed in the course of its evolution. This summary repe- 

 tition, by the individual, of the evolutionary progress of its 

 kind is known as the biogenetic law, and through its intelli- 

 gent application some of the most intricate problems in both 

 physiology and psychology have been solved. 



Practical Questions 



1. Does the biogenetic law throw any hght on the resemblances some- 

 times observed between leaves of different ages in unlike species; for 

 example, the fig and the mulberry? (170; Field Work, p. 195.) 



2. Can you name any other examples of plants or parts of plants which 

 show mutual resemblances in their early stages that do not exist at 

 maturity ? 



3. Are there other causes than those acting under the biogenetic law 

 to which some of these resemblances may be referred ; for instance, the 

 down and waxy coating on young leaves and bud scales? (148, 207.) 



VI. HYBRIDIZATION 



Material. — Several potted plants of tulip, lily, or any attainable 

 large flowered kind ; or preferably a small plot in a garden or nursery. 



Appliances. — A pair of dissecting scissors, a camel's-hair brush, and 

 some paper bags. 



Experiment 78. Does it make any difference whether a flower 



HAS its ovules FERTILIZED WITH ITS OWN POLLEN OR WITH THAT OF AN- 

 OTHER FLOWER OF THE SAME KIND ? — Carefully remove the unopened 

 anthers from a bud of a tulip, or other large flower just ready to unfold 

 (Fig. 331), inclose the mutilated bud in a small paper bag until the stigma 

 is mature, as shown by stickiness, then transfer to it with a camers-hair 

 brush some pollen from another flower. On the stigma of a second flower 

 of the same kind place some of its own jwUen, and cover with a paper bag 

 until the stigma withers, to keep foreign pollen from reaching it by means 



