86 



GROWTH AND WORK OF PLANTS 



nature, in the protoplasm.* The chlorophyll is a green pigment 

 in these bodies where it exists in numerous very fine grains. 



The chlorophyll bodies lie in the 

 outer layer of protoplasm, next 

 the cell wall. They are distributed 

 throughout the cells of the loose 

 parenchyma, the palisade cells, and 

 the guard cells, rarely in the epider- 

 mal cells (they occur in the epidermis 

 of ferns) and are absent from the 

 vascular bundles. 



2. MODIFICATIONS OF 

 LEAVES. 



146. The normal form of the 

 leaf, as stated in the previous 

 chapter, is a broad, thin organ 

 which thus exposes to the air and 

 light a great surface in comparison 

 with its bulk. This is because 

 the normal work of the leaf is 

 most advantageously and economi- 

 cally carried out with this form. 

 There are, however, numerous ex- 

 ceptions to this form presenting 

 what are termed modifications of 

 leaves in different plants. These 

 modifications are shown under a 

 variety of conditions: first, when 

 the leaf has entirely lost its normal 

 function; second, where a modification is demanded to enable the 



* Chromatophore is a general name for these bodies. They are capable of 

 division, and thus grow and multiply in the plant as the cells increase. 

 When devoid of color they are leucoplasts, when they have the chlorophyll 

 green they are chloroplasts, when they have red or yellow pigments they are 

 chromoplasts, as in the red and yellow petals of flowers, in the carrot, etc. 



Fig. 76. 



Indian pipe plant (Monotropa uni- 

 flora) with white stems and white scale 

 leaves. 



