Professor Sedgwick happened one day to mention a spring issuing from one of the chalk hills at Trumpington or Coton which deposited carb. of lime very prettily upon twigs &c. Darwin said to me, "I shall go and test that water for myself", which he did and found the fact to be as Sedgwick had stated it. Not content with this he deposited a large bush in the spring and at a subsequent lecture presented it to Sedgwick who exhibited it as being, what it really was, a very beautiful specimen. Several members of Sedgwick's class followed D's example and adorned their rooms with similar specimens of Increstation.
(Rodwell, John Medows. : [Recollections of Darwin in Cambridge.] )