Table 5—Plants, or Parts of Plants, Eaten by Captive Individuals of P. truei in Mesa Verde National Park, Colorado. 0 = not eaten, + = eaten, - = not offered.
| Species of Plant | Leaves | Stem | Flower | Seeds |
| Amelanchier utahensis | - | - | - | + |
| Calochortus gunnisonii | + | + | - | + |
| Chaenactis douglasii | 0 | 0 | - | - |
| Chrysothamnus depressus | 0 | 0 | 0 | - |
| Chrysothamnus nauseosus | + | 0 | 0 | - |
| Comandra umbellata | + | + | - | - |
| Erigeron speciosus | + | + | - | - |
| Eriogonum alatum | - | - | - | + |
| Juniperus osteosperma | - | - | - | + |
| Lupinus caudatus | 0 | 0 | + | - |
| Lithospermum ruderale | 0 | 0 | - | 0 |
| Mellilotus alba | + | + | + | + |
| Mellilotus officinalis | + | + | + | - |
| Orthocarpus purpureo-albus | + | + | + | + |
| Pedicularis centranthera | + | + | - | - |
| Penstemon linarioides | + | + | - | + |
| Pinus edulis | - | - | - | + |
| Polygonum sawatchense | + | + | - | 0 |
| Solidago petradoria | 0 | 0 | 0 | - |
| Viguiera multiflora | 0 | 0 | 0 | 0 |
Plant material eaten by captives of both species included Calochortus gunnisonii—stem and seeds; Comandra umbellata—leaves and stem; Eriogonum alatum—seeds; Penstemon linarioides—leaves and stem; Pinus edulis—seeds; and Juniperus osteosperma—seeds.
Plant materials refused by both species of mice included the leaves and stem of Chaenactis douglasii, the leaves, stem and seeds of Lithospermum ruderale, and the leaves, stem and flowers of Solidago petradoria.
Cricetine rodents chew plant and animal foods thoroughly; contents of their stomachs appear as finely-particulate fragments. These fragments invariably contain pieces of epidermis from ingested plants. Due to the presence of cutin in the cell walls, epidermis is last to be digested.
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 | + | + | - | - |