He married Agnes Theodora Walther , the daughter of Vilhelm Theodor Walther ) , in 1881 and his son is the botanist and sketch artist Vagn Petersson . In 1881 , he married Agnes Theodora Walther , daughter of Vilhelm Theodor Walther , and his son is the botanist and draftsman Vagn Petersson . He married Agnes Theodora Walther , daughter of Vagn Petersson in 1881 , and his son is the botanist and sketch artist Vilhelm Theodor Walther .