Although it is impossible to be certain, according to Marion Rayner of the British Bryological Society, the grey-green colours of the top study suggest that it is 'reindeer moss' (which is actually a lichen). The other study may be of another lichen, pamelia saxatilis. These types of lichen can easily be found growing luxuriously in Scotland and in other areas of the UK which have good air quality and high rainfall.

MacWhirter was a precociously talented artist who had a picture exhibited at the Royal Scottish Academy when he was only 14. These studies were made two years as a 16-year-old, before he became the extensively travelled and accomplished Scottish landscape painter he is now known as.