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A TEXTBOOK OF BOTANY [On. IV, 11 



case the stem acquires more chlorophyll, shown by a deeper 

 green color, thus supplementing better the work of the 



leaves; but in others the leaves 

 are reduced in size almost to dis- 

 appearance, leaving the foliage 

 function wholly to the slender- 

 cylindrical stems and petioles. 

 In others the stems become 

 flattened, thin, and green like 

 the leaves, as in the familiar 

 greenhouse plant Muehlenbeckia 

 (Fig. 139), the stem nature of 

 which, despite its deep green 

 color, is proven by the prominent 



FIG. 139. Muehlenbeckia platy- 

 clada; X f . (From Goebel.) 



nodes and the persistent 

 small leaves. Still more 

 striking are the cases in 

 which flattened stems, in 

 this case branches, be- 

 come limited in growth, 

 and assume characteristic 

 leaf shapes, to such a degree that their stem nature would 

 hardly be suspected at all, were it not that they grow from 



FIG. 140. Leaf-like cladophylla 

 (branches) of Butcher' s-B room, Ruscus 

 Hypoglossum, in the axils of bracts, and 

 bearing leaves and flowers ; X ^. (After 

 Kerner.) 



