The complex mixture of polymers coating the spore that protects the spore from dessication and UV radiation is:

Sporopollenin

Explanation:

Sporopollenin is a biological polymer that is highly cross linked and made up of oxygen, hydrogen and carbon. It is referred to a chemically inert biopolymer because of its toughness and stability in rocks that have been in existence for over 500 million years.  In other words, sporopollenin is chemically stable.

It is an important component of the outer layer or coating of pollen grains and plant spores. This protects spores from UV radiation and dessication.

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.