118 



WHY DO SEEDS GERMINATE? 



into an adult plant. Up to this stage of its existence it has had 

 the advantage of food and protection from the parent plant. Now 

 it must begin the battle of life alone. We shall find in all our work 

 with plants and animals that the problem of food supply is one 

 of the most important problems to be solved by the growing 

 organism. Let us see if the embryo is able to get a start in life 

 (which many animals get in the egg) from food provided for it 

 within its own body. 



Self-Testing Exercise 



The bean pod contains (1) which under favorable condi- 

 tions will (2). The (3) is the baby plant within the 



(4). Its parts are the (5), the (6), and 



the (7). The (8) contain the food supply for the 



(9). 



PROBLEM n. WHAT ARE THE TESTS FOR THE ORGANIC 

 NUTRIENTS FOUND IN SEEDS? 



Demonstration 1. Test for starch. Boil water with some laundry 

 starch in a test tube, then cool it, and add to the mixture two or three 



drops of iodine 1 solu- 

 tion. The mixture in 

 the test tube turns 

 purple or deep blue. 

 It has been learned 

 after many experi- 

 ments that starch is 

 turned purple or 

 dark blue by iodine. 

 Therefore, iodine so- 

 lution is used as a 

 test for the presence of 

 starch. 



Demonstration 2. 

 Test for oils. If a 

 substance is rubbed 

 on brown paper or is 

 placed on paper and 

 then warmed in an 

 oven, the presence of 



1 Iodine solution is made by simply adding a few crystals of iodine to 95 per cent 

 alcohol ; or, better, take by weight 1 gram of iodine crystals, f gram of iodide of 

 potassium, and dilute to a dark brown color in weak alcohol (35 per cent) or dis- 

 tilled water. 



diluted: 

 starch 

 -paste.. 



