Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:‚Äö√Ñ¬∂in cuticle thickness reported
 here is in agreement with other studies which show that cuticle thickness increases (e.g. Gratani and Bonito 2009; Varone and Gratani 2009) and wax formation continues (e.g. Bukovac et al. 1979; Gu√É√†lz et al. 1991; McWhorter et al. 1990) throughout leaf expansion.
Category: