PLANT PHYSIOLOGY 161 
of starch in a green leaf. Carefully describe, and sketch 
where possible, experiments you have performed to prove the 
following :— 
(2) That starch is formed by photo-synthesis only in green 
parts of plants. 
(b) That it is formed only when these parts are exposed to 
the light. 
(c) That the carbon di-oxide of the air is used in this starch- 
making. : 
(d) That this carbon di-oxide enters the leaves through the 
stomata. 
(e) That oxygen is given off during assimilation. 
15. (a) Draw as exact to life-size as you can a germinating 
seed, with its root marked so as to find out which part grows in 
length most rapidly. Draw it again as it would appear twenty- 
four hours later. 
(6) Explain how you would show that a leaf loses water 
chiefly through its stomata. 
16. How would you show that the presence of oxygen (or 
“fresh air’’) is necessary for the germination of seeds? 
17. Describe, in detail, experiments you have carried out to 
find out the answers to the following questions :— 
(a) What will happen if you grow a plant in a position where 
it can get light from one side only ? 
(b) What causes a root to grow downwards and a stem to . 
grow upwards? =” 
(c) Which side of an ordinary foliage leaf gives off most 
water ? 
(d) “Green leaves make starch in the light.” What happens 
in the case of a leaf which is partly green and. partly white? 
(Mention the plant used in carrying out this experiment.) 
18. Carbon and nitrogen are known to be essential elements 
to a plant. Describe experiments to show whether these ele- 
ments are obtained by the plant from the soil or from the air, 
giving an exact and detailed deseription of how the experiments 
you describe were set up and the results obtained from each. 
19, Describe and explain the appearance of a seedling which 
has been supplied with air and moisture, but has been kept in 
the dark. 
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