THE YOSEMITE FLORA 5 



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our district, the result is a forest, with us a coniferous forest. 

 When, however, the moisture is near the surface, as in many val- 

 leys and around springs, the result is, not a forest, but a meadow. 

 When a group of trees occurs in a meadow, it indicates that the 

 moisture at that spot is deeper in the soil ; in fact, such forest 

 islands are, in most cases, plainly seen to be situated on land 

 which is slightly more elevated or better drained than the sur- 

 rounding areas. 



It sometimes happens, especially on warm, well-drained slopes, 

 that the moisture-content of the soil is too small for either 

 meadows or forest, in which case a chaparral formation may 

 result. This consists of low shrubs, usually with deep roots and 

 with, other characters which especially adapt them to dry situ- 

 ations, as has been pointed out in considering the Foothill Belt. 

 The thickets of Chinquapin, Huckleberry Oak, Manzanita, etc., at 

 considerable altitudes, also belong to the chaparral formation and 

 are always found where soil moisture is comparatively scarce. 



Other formations which may be traced out by the interested 

 student include that of the stream banks, known as the riparian 

 formation. Around and especially in the quiet ponds and lakes 

 another type of vegetation will be encountered; still another on 

 the crests and summits; and so a dozen or more distinct forma- 

 tions may be recognized, each made up of forms particularly 

 adapted to that special environment. 



That external conditions exert a profound influence on the 

 structure and appearance of plants is well known. We have 

 already seen that those growing in dry places have special de- 

 vices for acquiring and retaining moisture. As contrasted with 

 these it will be noted that plants growing in moist situations, as 

 along streams, around lakes or springs, and in shady places are 

 devoid of such adaptations; the root system is often shallow, the 

 leaves are broad and without hairy or resinous coats, the stems 

 are taller and without spines or thorns. 



Such plants as we have just described often owe their charac- 

 ter not only to an abundance of water, which is the most influen- 

 tial factor affecting the shape of plants, but also to the absence of 

 excessive light. Shady places are usually moist places, and it is 

 sometimes difficult to determine whether certain characters are 

 the result of the moisture or of the light relation. Often they re- 

 sult from both factors operating at the same time. Leaves ex- 

 posed to strong sunlight not infrequently assume a vertical posi- 

 tion, thus presenting but a small surface to the sun's rays, as may 

 be seen in some manzanitas. On high mountains, where the light 

 is very intense, leaves are provided with a thick epidermal layer 

 which. doubtless serves for purposes of protection. Plants in the 



