THE CHLOROPLASTS 



141 



The first visible food made by the chloroplasts is slarrh in 

 the form of very minute grains (Fig. 71). There is reason 

 to believe that sugar is 



formed before the starch 

 appears, and presumably 



^^ 



Fig. 71. — Starch grains from the palisade cells 

 of a Euphorbia leaf, magnified about 1800 diameters. 



in the chloroplasts also, 

 but it is soluble in the cell- 

 sap and probably does not 

 long remain where it is 

 first formed, but passes by 

 diffusion from the chloro- 

 plasts into the cell-sap that 

 fills the cell cavity, and 

 thence into the tissues de- 

 voted to food-conduction, 

 as told in the next chapter. 



The minute size of the chloroplasts affords them large surface 

 in proportion to their volume, and this gives a great advantage 



in the absorption of raw materials 

 and energy, and in the elimination of 

 the finished product. 



The chloroplasts are always em- 

 bedded in the cytoplasm close against 

 the cell-wall, and this peripheral posi- 

 tion is apparently an advantage to 

 every phase of their work; for, as 

 Fig. 72 will show, on one side water 

 is presented to the chloroplasts from 

 the cell-sap, and on another carbon 

 dioxide from the intercellular spaces,, 

 and the vacuole affords an unob- 

 structed way for the removal of the 

 manufactured product. Also by this 

 arrangement the light entering the leaf 

 from all parts of the sky has a clearer path to every chloroplast 

 throughout the leaf than would otherwise be the case (Fig. 73). 



Water O 

 Pood 



Fig. 72. — Diagram to show the 

 intake of carbon dioxide by the 

 palisade cells from the inter- 

 cellular spaces, the absorption by 

 the chloroplasts of water from 

 the cell-sap, and the passage of 

 food from the chloroplasts into 

 the cell-sap. The palisade cells 

 are shown in cross section, as they 

 would be if the leaf were cut 

 parallel with the surface, namely, 

 tangentially. 



