Though many Dadaist and Surrealist artists were practicing poets, Arp is one of the very few whose poetry stands in both quality and quantity as an important contribution in its own right. The involvement of the painters of these movements with poetry produced a variety of rapports between the two arts, some of which endowed their peinture-poésie with new and unexpected dimensions, but others of which tended to vitiate their painting through a dilution of aesthetic modes. Arp's collages, reliefs, and sculpture share with his poetry an iconography...a gentle whimsy, and a feeling of naturalness, but nowhere is their plasticity compromised.
For three years prior to the emergence of his personal style in the winter of 1915/1916, Arp had worked within the discipline of Cubism. Then in collages, and in machine-sawn reliefs such as the Portrait of Tzara of 1916 and Enak's Tears of 1917, the prevailing rectilinear structures of the Cubist work dissolved under the pressure of a new curvilinear, "organic" morphology.
This biomorphism had its roots in Art Nouveau, although there it was primarily linear in style and botanical in its associations. Arp established it in terms of closed flat forms that were endowed with anthropomorphic allusions as well....
In the face of Analytic Cubism's searching but ultimately assured equilibrium and stasis, Arp's reliefs unwind in an improvisational, meandering manner that implies growth and change. Here is no longer the sober, classical scaffolding of the external world of architecture. The forms of the Portrait of Tzara and Enak's Tears, while describing nothing specifically, multiply associations to physiological and botanical processes, to sexuality, and through their very ambiguity, to humor.
Although biomorphism initiated a new vocabulary of forms, it did not in itself constitute a style in the sense that Impressionism or Cubism did; nor did it generate any new comprehensive principle of design or distribution of the total surface, or of the illusion of space, in pictures. Rather it provided constituent shapes for paintings in a variety of styles. When more than one or two such shapes are used by the "abstract" Surrealists we almost always find them disposed in relation to one another and to the frame in a Cubist manner. Thus, while we may speak of the form-language or morphology of Arp, [André] Masson, and [Joan] Miró as anti-Cubist, this does not apply to the over-all structure of their compositions, since on that level these painters cling to organizational principles assimilated from the Cubism that all of them had practiced earlier.
from William S. Rubin, Dada, Surrealism, and Their Heritage, New York: The Museum of Modern Art, 1968, p. 39–41