This drawing is about mathematics and nature, the long branching stems of Rhipsalis cereuscula reminded me of the structure of probability trees, so this particular specimen grew a probability tree of having a specific blood type and rhesus factor.

Graphite and colour pencil on paper, textured background added later.

Ink on paper, colour pencils, computer edited backgrounds. 

'Validation'

Ink on paper rendered in Photoshop

Pencil drawing of an exhibit in museum in Helsinki rendered with Photoshop.