410 



RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. 



leaved stem. The lowest leaves originating next the soil are the longest; the leaves 

 next above these are, on the other hand, visibly shorter, and often in the region of 

 the flowers are changed into insignificant scales closely applied to the stem. It can 

 easily be seen in every plant of the Shepherd's Purse {Caf sella Bv/rsa pastoris), on 

 every mullein (Verbascum), and every hawkweed (Hieraciuvi), that such small 

 upwardly-directed leaves cannot injure by overshadowing the leaves growing below 

 them either in the same or in adjacent rows. 



Fig. 103.— Leaf-mosaic 



1 Leaf-rosettes of a Crane's-bill {Geraniuin Pyrenaicum) seen from above. 2 Leaf-rosettes of a Saxifrage (Saxi/raga Aizoon). 

 ' Leaf-rosette of a Bell-flower {Campanula pusilla) seen from above. * Adpressed scale-like leaves on the twig of an 

 Arbor Vitaj {Thuja). 



Many plants produce within a year, at the ends of their upright shoots, a large 

 number of leaves which radiate out from the stem with very small horizontal 

 divergencies, standing close above one another, and forming a so-called rosette. In 

 order that all the leaves of such a rosette may receive an equal proportion of light, 

 it is absolutely necessary that the upper leaves should be considerably shorter than 

 the lower. And in all rosettes this is actually the case. However, some very 

 interesting modifications are to be seen. In rosette-forming succulent plants (e.g. 

 Echeveria and SempervivUTn), and in many saxifrages {Saxifraga), of which a 

 species (Saxifraga Aizoon) is represented in fig. 103 ^ the leaves are tongue-shaped 

 or spatulate, and about twice as broad near the further end than at the point of 



