FOLIAGE LEAVES : THE LIGHT-RELATION. 



17 



smaller and less horizontal toward the apex of the stem 

 (see Pigs. 10, 13). The common sheijherd's purse and the 

 mullein may be taken as illustrations. By this arrange- 

 ment all the leaves are very 

 completely exposed to the 

 light. 



21. The rosette habit. — 

 The habit of producing a 

 cluster or rosette of leaves 

 at the l)ase of the stem is 

 called the rosette habit. 

 Often this rosette of leaves 

 at the l)asf!, frequently lying 

 flat on the ground or on the 

 rocks, includes the only fo- 

 liage leaves the plant pro- 

 duces. It is evident that a 

 rosette, in which the leaves 

 must overlap one another 

 more or less, is not a very 

 favoraljle light arrange- 

 ment, and therefore it must 



be that something is being 



Pig. 10. A plant (Erhcreriii) with fleshy 

 leaves, showing large horizontal ones 

 at base, and olhtTs becoming smaller 

 and more directed upward as the 

 stem is ascended. 



provided for besides the 

 light-relation (see Figs. 11, 

 1-2, 13). What this is will 

 appear later,, but even in 



this comi)aratively unfavorable liglit arrangement, there is 

 evident adjustment to secure the most light possible under 

 the circumstances. The lowest leaves of the rosette are 

 the longest, and the ujiper (or inner) ones become gradu- 

 ally shorter, so that all the leaves have at least a part 

 of the surface exposed to light. The overlajDped base of 

 such leaves is not expanded as much as the exposed apex, 

 and hence they are mostly narrowed at the base and broad 

 at the apex. This narrowing at the base is sometimes 



