FOLIAGE LEAVES : THE LIGHT-RELATION 



17 



smaller and less liorizontal toward tlie apex of the stem 

 (see Figs. 10, 13). The common shepherd'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 base of the stem is 

 called the rosette hahit. 

 Often this rosette of leaves 

 at the base, 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 

 favorable light arrange- 

 ment, and therefore it must 

 be that something is being 

 provided for besides the 

 light-relation (see Figs. 11, 

 12, 13). AVhat this is will 

 appear later, but even in 



this comparatively unfavorable light arrangement, there is 

 evident adjustment to secure the most light possible undo 

 the circumstances. The lowest leaves of the rosette are 

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

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

 of the surface exposed to light. The overlapped 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 



Fig, 10, A plant (Echeveria) with fleshy 

 leaves, showing large horizontal ones 

 at base, and others becoming smaller 

 and more directed upward as the 

 stem is ascended. 



