RELATION BETWEEN POSITION AND FOBM OP GREEN LEAVES. 



insertion upon the abbreviated axis. It is unavoidable that ^ 

 proximal halves of most of the leaves should be covered by the leaves aZeTd 



hi I' 7 T T 1 * %ht ^ theS6 C Vered P rtions 1y deZLof 

 chlorophyll and so have no need of direct sunlight. The distal halves, on the ol 



which display green tissue, can by this arrangement be all well illud 

 s,mu taneousy by the sun. In many other instances the increase in length is 

 found m the leaf-stalks of the lower leaves of the rosette. These increase in length 

 that u, to say, until the blades borne by them are moved out of the shadow of "the 



Fig. 104. Formation of a Leaf -Mosaic by the lengthening (relative shortening) of the Leaf-stalks, 

 i Small-leaved Balsam (Impatiens parviflora). a Green Amaranth (Amarantu* Blitum). Thorn-apple (Datura Stramonium). 



leaves above. This is the case, for example, in the leaf-rosettes of Geranium 

 Pyrenaicum, represented in fig. 103 \ and in the leaf -rosettes of the dainty little 

 bell-flower (Campanula pusilla, fig. 103 3 ) growing on the debris-covered slopes of 

 the sub-alpine regions. In these bell-flowers the great difference in shape between 

 the rosette-leaves and those clothing the flower-stalk is worthy of remark. The 

 latter, which spring at an acute angle from the stem, are narrowly lanceolate, and 

 have very short stalks, while the lower rosette-leaves, extended flatly over the soil, 

 have long stalks, and possess a broad, ovate blade. It is no disadvantage to the 

 leaf -stalks, which have no chlorophyll, if they are placed in the shade. But by this 

 arrangement all the broad, green leaf-blades are well illumined, and this applies 

 also to the more loosely-arranged, upwardly-directed, narrow leaves of the stem. 



