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 light 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 
Mareriau. — 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. Dorks 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 camel’s-hair 
brush some pollen from another flower. On the stigma of a second flower 
of the same kind place some of its own pollen, and cover with a paper bag 
until the stigma withers, to keep foreign pollen from reaching it by means 
