LEAVES 



211 



Perhaps the most common method of protection used by 

 small plants growing in exposed situations, as bare rocks and 

 sandy soil, is the rosette-habit ( 123, p. 200) (Figs. 163 and 164). 

 The clustered leaves, flat upon the ground or nearly so, and 

 more or less overlapping, form a very effective arrangement 

 for resisting intense light or drought ; but it must be remem- 

 bered that it is not an 

 effective arrangement of 

 leaves for work, it is only 

 an effective arrangement 

 for protection, so that 

 work may go on in un- 

 favorable conditions. 



A position developed 

 by the leaves of some 

 plants in regions of in- 

 tense light is the profile 

 position, and such leaves 

 are called profile leaves, 

 a margin being directed 

 upwards and the leaves, 

 in this way, standing 

 edgewise. This position 

 results in turning away 

 the faces of the leaves 

 from the intense rays of 



. , , , . FIG. 177. Prickly lettuce, showing the profile 



midday and exposing (edgewise) leaves from two points of view. 



them to the morning and 



evening rays of less intensity. In the dry regions of Australia 

 the leaves of many of the forest trees and shrubs are profile 

 leaves, giving to the foliage a very peculiar appearance. The 

 best known illustration of a plant in this country with profile 

 leaves is the " compass plant," a rosinweed of the prairie 

 region. Its name was given because its edgewise leaves were 

 observed to point in a general north and south direction, 



