The pedagogical problem of illustrating textbooks for the Basic Nine Year School became topical towards the end of the fifties and at the beginning of the sixties. At that time the outward effect of the colour scheme in the text was overestimated, which caused the actual purpose and aim of the graphic make-up to be disregarded. The problems involved were the subject of a theoretical assessment by Academician O. Chlup, who defined the didactic function of textbook illustrations. He demands that illustrations serve, above all, the educational purposes of the textbooks. He regards as a drawback the efforts to facilitate the comprehension of abstractions by means of illustrations because abstractions cannot be represented graphically. He underlines this idea by the fact that abstract thought is going along different nerve links conditioned by the associations of the higher nervous activity and their deeper understanding is not helped by illustrations. Chlup points out that the main principle of the graphic and illustrative art in textbooks is the adequacy in the choice of artistic media. Too many colours distract attention and often become commonplace and lead to listlessness. In this respect Chlup was a follower of Hostinský’s aesthetics, which paid due attention to the development of good taste, aesthetic experiences and artistic impressions. Chlup’s Ideas concerning the aesthetic make-up and illustrations of textbooks induced František Holešovský to investigate the function of colours and its hygienic, psychological and didactic effect on the youth. The research has helped to formulate certain theses clarifying the problems of textbook illustration in connection with a general arts education of the youth in schools. This has also evoked responses in specialist literature where critical comments have been published. Under the influence of Academician O. Chlup modern pedagogy in our country has begun to deal with the question of the didactic and aesthetico-educational role of textbook illustration as a useful medium of educational practice, illustration is not an arbitrary counterpart to the content of the text but its organic component.