116 WHY DO SEEDS GERMINATE? 



Two sets of factors are necessary for the growth of seeds: 

 first, the presence of food substances inside the seed in order to 

 give the baby plant a start in life ; and, secondly, certain stimulat- 

 ing factors outside the seed, such as air, moisture, and warmth. 

 Experiments which you can do yourself and observations you can 

 make in almost any garden show the necessity of these factors 

 very clearly. One value you will get from this unit will be the 

 opportunity you have for determining, by means of certain simple 

 experiments, the factors which control the beginnings of growth 

 in a seed. 



It is a trite but true saying that we grow because we use food. 

 The same is true of plants. Certain food substances, the organic 

 nutrients (such as carbohydrates, fats, and proteins), are found 

 in seeds. We eat peas and beans. If we test these seeds, we can 

 show the presence of foodstuffs within them. The pea or bean 

 seedling uses the locked-up energy within the foods in order to 

 break out of the seed coat and force their growing roots and stems 

 through the soil. The little plants also grow in size. This indi- 

 cates quite clearly that some of the nutrients within the seed are 

 transformed in some mysterious manner into the living material 

 out of which the plant is built. Later we shall be able to make a 

 comparison of the manner in which these nutrients are used by the 

 plant with the way in which we use these same food substances. 

 It will be sufficient to say here that the foods which are really 

 outside of the baby plant must be changed from a solid food sub- 

 stance into a liquid form so that the cells out of which it is formed 

 may absorb the food substances into their own bodies. This 

 process of changing insoluble foods into soluble food substances 

 is called digestion. 



PROBLEM I. WHERE ARE BABY PLANTS FOUND? 



Laboratory Exercise. Make a drawing of a bean pod. Mark all 

 the parts of the flower that you can find in it. What is a pod? Now 

 open the pod and examine the seeds. How are they attached? 

 Remove a bean, open it, and find the tiny future stem and leaves of 

 the baby plant between the two " halves " of the bean called the 

 cotyledons. Referring to the next paragraph, draw and label all the 

 parts of the bean seed. 



