Ruskin here refers collectively to Rogers's Italy (1830) and Rogers's Poems (1834), both of which were illustrated by steel-engraved vignettes after Turner. (See Ruskin and Turner's illustrations to Rogers's Poems, and also Ruskin, Turner, and engraving.)
In Praeterita, Ruskin records the importance of these illustrations for him as a youth preparing for his first visit to Italy: 'the artificial taste in me had been mainly formed by Turner's rendering of those very scenes, in Rogers' Italy. The "Lake of Como,'' the two moonlight villas, and the "Farewell" had prepared me for all that was beautiful and right in the terraced gardens, proportioned arcades, and white spaces of sunny wall' ( Works, 35.117). (See Lake of Como, the two moonlight villas and A Farewell - Lake of Como (II).)
The 'artificial taste' of which Ruskin speaks does not imply a lack of naturalistic truth in these vignettes: for example, elsewhere in Modern Painters 1, Ruskin explains how the Lake of Como vignette illustrates 'the great principles of cloud form' (MP I:234).