Fuction of thick cuticle

The primary function of the plant cuticle is as a water permeability barrier that prevents evaporation of water from the epidermal surface, and also prevents external water and solutes from entering the tissues. In addition to its function as a permeability barrier for water and other molecules (prevent water loss), the micro and nano-structure of the cuticle confer specialized surface properties that prevent contamination of plant tissues with external water, dirt, and microorganisms. Dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica and in the sporophytes of all vascular plants. In angiosperms the cuticle tends to be thicker on the top of the leaf (adaxial surface), but is not always thicker. The leaves of xerophytic plants adapted to drier climates have more equal cuticle thicknesses compared to those of mesophytic plants from wetter climates that do not have a high risk of dehydration from the undersides of their leaves."The waxy sheet of cuticle also functions in defense, forming a physical barrier that resists penetration by virus particles, bacterial cells, and the spores and growing filaments of fungi".