Final answer:
The images painted between 1908 and 1913 likely demonstrate 'Mondrian's development toward increasing pictorial abstraction,' reflecting the movement of modernist art away from representational forms.
Step-by-step explanation:
The question pertains to the demonstration of "pictorial abstraction" as seen in the paintings dated between 1908 and 1913. Considering the broader historical context of modernist movements, such as Fauvism, Expressionism, Cubism, the emergence of Abstract Expressionism, and the influence of Surrealism and Dada, as well as the impact of individual artists like Wassily Kandinsky and Piet Mondrian, it is clear that the works signify "Mondrian's development toward increasing pictorial abstraction." The progression towards abstraction is a hallmark of Mondrian's work, parallel to the evolution of European modernist art during that period, which progressively moved away from realistic representation towards more abstract and conceptual forms. The discussion of various modernist styles and artists sets the background against which Mondrian's transition to abstraction can be understood.