6 THE YOSEMITE FLORA 



full glare of the sun have, almost without exception, narrow or 

 especially protected leaves, thus guarding against excessive light, 

 which might destroy contents of their live tissues, and at the 

 same time protecting themselves from excessive withdrawal of 

 moisture through their pores. 



As contrasted with these light-tolerant species, it is interesting 

 to examine the shade-loving plants. Here we find an abundance 

 of foliage, the broad, smooth, and thin leaves being spread out in 

 such a manner as to receive the full benefit of the diffused light 

 sifted through the upper layers of the vegetation. Even the 

 arrangement of the leaves so as to prevent overlapping is as 

 though planned with the greatest of care. The Enchanter's 

 Nightshade is a good example, the leaf-blades being broad and 

 exceedingly thin. The Monkshood, Columbine, Twayblade, 

 Meadow-rue, and Thimble Berry are other instances. The leaves 

 of the Twinberry, «a plant of shaded places, are decidedly thinner 

 than those of the manzanitas of our exposed slopes. 



Rock-plants have exceptionally adverse conditions with which to 

 contend. Aside from the great exposure to light, the soil from 

 which their nourishment is drawn is very shallow and is moistened 

 only during rains. Many of these plants, such as the Stonecrops, 

 have acquired a fleshy habit, the thick, juicy leaves and stems 

 being filled with water in time of plenty to provide for their needs 

 in time of drought. The epidermal layers are smooth and tough 

 and with but few openings. 



Such adaptations to environment as we have been considering 

 result not only in a varied aspect of the vegetation as a whole, 

 but often produce so great a change in the appearance of plants 

 belonging to one species that even trained botanists are deceived. 

 Many a supposedly "good new species" has been named and de- 

 scribed which farther observation has shown to be only an 

 extreme form of a well-known species, the result of an unusual 

 environment. The common Monkey-flower is one of these plastic 

 species. Under favorable conditions it grows to heights of two or 

 three feet, producing many large leaves and flowers, yet it varies 

 into forms only two or three inches high, with minute leaves and 

 flowers "scarcely large enough to measure." This pygmy form is 

 common around the Yosemite, especially on very shallow soil 

 underlaid with granite, and all intermediate stages may here be 

 observed. Other examples might be cited, where variation ex- 

 tends not only to shape and size but to color, amount of 

 pubescence, lobing of leaves, and many other characters, all of 

 which greatly affect the appearance of a plant. In searching for 

 an explanation of these variations the investigator must consider, 

 not one or two, but all of the possible factors. 



