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M. Hülskamp is the first author of a 1994 study using mutants to dissect trichome development in Arabidopsis thaliana. The investigators isolated and characterized more than $70$ mutants representing $21$ genes, then compared the shapes and developmental phenotypes of their specialized epidermal cells.^[ref]

The phenotypes helped distinguish events contributing to mature-cell architecture. Although these events normally occur in a temporal sequence, the genetic comparisons indicated that much of the final form is assembled through partly independent processes.^[ref]

This illustrates how an observed sequence can differ from a strict chain of necessities. If one feature is altered while another still forms, the earlier feature need not be the only route by which the later one is produced. Comparing multiple mutants therefore reveals relationships that a movie of normal morphogenesis alone would not establish.

A trichome is an outgrowth of the plant epidermis, often appearing as a hair or scale. Its cellular construction and function depend on the plant. The specialized epidermal cells on Arabidopsis thaliana leaves and the elaborate surface scales of Tillandsia usneoides illustrate why one shape or one role should not define every trichome.

A 1994 genetic study isolated more than 70 trichome mutants representing 21 genes in Arabidopsis thaliana. Comparing their cellular phenotypes separated contributions to morphogenesis, rather than treating the mature cell's architecture as one indivisible property.^[ref]

A different experimental question concerns function. In Tillandsia usneoides, intact flexible trichome wings supported surface water spreading more effectively than preparations without those wings. Fluorescent imaging and deformation observations connected the wing array with propagation of a water film.^[ref]

These examples separate the formation of a structure from what it does. A mutation changing a cell's form can identify a developmental contribution; removing or altering a surface feature while measuring water movement tests a mechanical contribution. Neither result requires every hairy plant surface to use the same genetic program or solve the same ecological problem.