1044 



A TEXTBOOK OF THEORETICAL BOTANY 



definitely specialized cataphylls and they function almost wholly as reserve 

 organs, not for assimilation. 



Succulent plants often have fleshy leaves which store water. The normal 

 mesophyll is replaced in such leaves by two zones of cells, one towards the 

 upper surface, which is relatively shallow and is composed of small parenchyma 

 cells containing chloroplasts, and another much deeper zone, making up 

 the bulk of the leaf, which consists of very large, thin-walled cells with no 

 chloroplasts, in which the water is held (Fig. 1039). 



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Fig. 1039. — Pepei otnia sp. Transverse section of leaf showing 

 chlorophyll-containing tissue limited to the upper part of 

 the lamina and large-celled water storage tissue below. 



4. Ascidial Leaves. — These are specialized leaves in which the lamina is 

 not flat but encloses a sac-like space (Fig. 1040). They are usually the result 

 of overgrowth of one side of a dorsiventral leaf and may, therefore, be regarded 

 as extreme cases of rolled leaves, or even as related to unifacial centric leaves 

 (p. 1019). Ascidial leaves may occur as abnormalities {e.g., in Rosa), but where 

 they are normal developments in a species, they are almost always associated 

 with some specialized life conditions, such as insect capture, water storage, 



