Microscopic analysis of plant epidermis is useful in helping to determine food habits of various animals (Dusi, 1949; Williams, 1955, 1959a; Brusven and Mulkern, 1960; Johnson, 1962). The microscopic analysis of stomach contents provides a practical method of determining which plants are eaten by rodents. Contents of stomachs and intestines were removed from mice caught in snap traps, and from preserved specimens. The contents were placed on a piece of bolting silk, washed thoroughly with running water, stained with iron-hematoxylin and mounted on slides, or stored in 70 per cent ethanol (Williams, 1959a; Douglas, 1965). TABLE 6--Plants, or Parts of Plants, Eaten by Captive Individuals of _P. maniculatus_ in Mesa Verde National Park, Colorado. 0 = not eaten, + = eaten, - = not offered. =============================+========+======+========+======= Species of Plant | Leaves | Stem | Flower | Seeds -----------------------------+--------+------+--------+------- _Artemisia ludoviciana_ | 0 | 0 | - | - _Calochortus gunnisonii_ | 0 | + | - | + _Chaenactis douglasii_ | 0 | 0 | - | - _Comandra umbellata_ | + | + | - | - _Erigeron speciosus_ | 0 | 0 | - | - _Eriogonum alatum_ | - | - | - | + _Juniperus osteosperma_ | - | - | - | + _Lappula redowskii_ | 0 | 0 | - | + _Lithospermum ruderale_ | 0 | 0 | - | 0 _Orthocarpus purpureo-albus_ | 0 | 0 | + | + _Penstemon linarioides_ | + | + | + | - _Pinus edulis_ | - | - | - | + _Purshia tridentata_ | + | + | - | - _Sitanion hystrix_ | 0 | 0 | - | 0 _Solidago petradoria_ | 0 | 0 | 0 | - _Sphaeralcea coccinea_ | + | + | - | + _Stipa comata_ | 0 | 0 | - | + _Viguiera multiflora_ | + | + | - | - -----------------------------+--------+------+--------+------- In order to analyze these epidermal fragments, a collection of plants was made within the park. Slides of the epidermis of these plants were prepared and analyzed for diagnostic characters (Douglas, 1965:197-199). Features such as the stomatal arrangement in relation to subsidiary cells; the types of trichomes, scales and glands; the cellular inclusions such as starch grains, mucilage and resins are of taxonomic value (Metcalfe and Chalk, 1950). The configuration of the anticlinal cell walls is useful in separating species that are similar in other respects (Douglas, 1965:199). The following species of plants, and other food items, were identified in the stomach or intestinal contents of _Peromyscus maniculatus_: