162 SOUTH AFRICAN BOTANY 
20. Write an essay on ‘‘ Protective Adaptations against Dry- 
ness,” illustrating it throughout by reference to. your own 
observations on plants which show such adaptations. Say 
where you saw each plant you mention ; e.g. on veldt, mountain 
or sea-shore (where ?), in school garden or as a preserved speci- 
men pictured in a book (what book ?) ete. 
21. State what you know as to the movement of sap in the 
stem. 
22. Explain fully the functions performed by chlorophyll 
in a plant. 
23. State what you know of the processes referred to in the 
following sentence: ‘‘Experiments have shown that carbon 
di-oxide is absorbed and that oxygen is given off by all green 
surfaces of plants during the hours of sunlight”. 
24. In what form and for what purpose are the following 
elements appropriated by plants: carbon, calcium, sulphur, 
nitrogen, oxygen. 
25. From what source and in what forms do green plants 
usually absorb their nitrogenous food? Mention cases in 
which the nitrogenous food is absorbed from other sources 
and in other forms. 
26. Say what you know about the absorption of liquids by 
plants. What are the chief organs concerned in the process in 
the case of the higher plants? Enumerate the themical ele- 
ments which are essential to the nutrition of green plants and 
explain how such plants are enabled to* absorb substances 
which are insoluble in water. 
