Asci of Ascobolus
In the young ascus (left) you can see the nucleus at the centre of each developing ascospore. In the mature ascus (right) the ascospores have become thick walled and pigmented to protect them from u/v (solar) radiation and other environmental stresses. The lines you see on the spores are thin spots in the walls (germ slits). This allows the spore to monitor the outside environment and germinate at a favourable opportunity.