LEAVES AND LEAF STRUCTURE 93 



found in the form of very minute particles called chlorophyll 

 grains, or chloroplasts, which seem to consist of active protoplasm 

 combined with the green chlorophyll. This is the substance which 

 performs the essential function of the leaves. It is found mainly 

 in the palisade cells and spongy layer. The former are arranged 

 to regulate its exposure to light, and the latter to provide it with 

 carbon dioxide and water to use in starch making. We shaU devote 

 the next chapter to the way in which it does its work. For the 

 present, think of chlorophyll as occurring in the form of active, 

 green grains, found in all green parts of plants and very essential 

 to their growth. 



SUMMARY 

 Functions : 



1. Starch making. 



2. Digestion and assimilation. 



3. Respiration. 



4. Excretion. 



5. Reproduction. 



General structure: 



1. Blade. 



2. Petiole (leaf stalk) attached at nodes. 



3. Veins (duct bundles). 



Functions, support and transportation. 

 Arrangement : 

 Parallel (grasses). 

 Netted: 



Feather veined (elm). 

 Finger veined (maple). 



4. Outline. 



Irregular margin in netted veined leaves. 

 Regular margin in parallel veined leaves. 



Adaptation for exposure to light and air: 



1. Shape, so as to let light through to others. 



2. Arrangement, opposite or alternate. 



3. Heliotropism. 



Positive in leaves and flowers. 

 Negative in roots. 



Modified leaves, as 



1. Tendrils, for climbing (pea). 



2. Thorns for protection (barberry). 



3. Thickened, for storage (cactus). 



4. Traps, for catching insects (sun-dew). 



