How does Muriel Spark use imagery in The Prime of Miss Jean Brodie?

Imagery:

‘I am putting old heads on your young shoulders,’ Miss Brodie had told them at that time, ‘and all my pupils are the crème de la crème.’

‘It has been suggested again that I should apply for a post at one of the progressive schools, where my methods would be more suited to the system than they are at Blaine. But I shall not apply for a post at a crank school. I shall remain at this education factory. There must be a leaven in the lump. Give me a girl at an impressionable age, and she is mine for life.’