THE BEAN 



117 



The bean. If we open a bean pod, we find the seeds lying 

 along one edge of the pod, each one attached to the inner wall at 

 the placenta by a little stalk through which it gets its nourishment. 



remains of stigma 

 _..seecL 



-.-plctCenbcx 



..Valve of pod 



The stalk leaves a scar on 

 the coat of the bean, called 

 the hilum (hi'tam). The 

 tiny hole near the hilum 

 is the micropyle (mi'krO- 

 pil). Turn to the diagram 

 on page 85, showing the 

 fertilization of an ovule. 

 Find there the little hole 

 through which the pollen 

 tube reached the embryo 

 sac. This small structure, 

 the micropyle, remains 

 and is found in the seed. 

 The thick seed coat, the 

 testa, is readily removed 

 from a soaked bean. The 

 seed then separates into 

 two parts : the cotyledons 

 or seed leaves. The rodlike part between the cotyledons is called 

 the hypocotyl (hl'pS-kot'il) . This will later form the root and 

 part of the stem of the young bean plant. The first true leaves, 

 very tiny structures, are folded together between the cotyledons, 

 and, with the future stem, are known as the plumule (ploo'miil). 

 All the parts of the seed within the seed coats form the embryo 

 or young plant. A bean seed contains, then, a tiny plant pro- 

 tected by a tough coat. 



Practical Exercise 1. Using a number of seeds, show to the class the pres- 

 ence of an embryo in each. Does it occupy the same position in each case? 

 Write in your notebook a good definition of a seed. 



Food in the cotyledons. The laboratory work shows us that 



a seed really contains a baby plant or embryo, with a sufficient 



supply of food to give it a start in life. The problem now before 



us is to find out how the embryo of the bean is adapted to grow 



H. bio — 9 



A pod opened to show attachment of seeds, 

 the parts of the flowers. 



Find 



