Our tutor was Oliver Gilbert (of lichens and air pollution) who had us throw quadrants comparing Nardus and Sesleria grassland. In the former grew Galium saxatile in the latter G .sterneri. We didn't have hand lens but holding the leaves against a wet finger you can actually see the direction of the marginal hairs with the naked eye. That day I learned about calcicoles and calcifuges and that the 2 Galium species are good indicators. 11 years ago, in an attack of atavism on my 60th birthday, I revisited the sites to refind all the species I'd seen so many years before.
The point of this memory is that it helped to set me on the path to becoming a professional botanist where identification skills have been absolutely vital to my research projects on the biology and evolution of land plants.
Also on that field course was my school contemporary Roger Hughes. He was fired up by another excursion that looked at invertebrate zonation in the Tarn,under the tuition of Paul Holmes. The wet finger technique was invaluable here to separate smooth and ridge-shelled Planorbis. Roger went on to become professor of zoology at Bangor and a world authority on Bryozoa.
In 1964 as an undergraduate I saw >250 bryophytes on another Malham Tarn course run by Michael Proctor.