40 



INTRODUCTION TO BOTANY 



Often green plants make more food than they use at the 

 time, and this surplus food may be stored or reserved in some 

 way. Stored food may or may not be used later by the plant, 

 and may oftentimes become the food of other plants, of ani- 

 mals, or of men. 



38. Food transported by the plant. In all except the sim- 

 plest plants the reserve food is carried from the cells in which 

 it was manufactured, into other cells. In plants with fleshy 

 leaves, like the houseleek, the century plant, the common purs- 

 lane, and many others, the greater 

 part of the stored starch and other 

 nutritive materials has only been car- 

 ried to the leaf interior from the outer 

 portions of the leaf, where photosyn- 

 thesis and other manufacturing proc- 

 esses go on. The distance traversed 

 may be only a small fraction of an 

 inch, but in case much of the food is 

 stored in underground parts of the 

 plant, it may have been carried for 

 long distances in large trees, some- 

 times more than a hundred feet before 

 it reaches the root at all. 



39. Form in which food is transported. As already stated, 

 one of the products of photosynthesis in most plants is starch. 

 This is deposited in or about the chloroplasts, during their 

 exposure to daylight, in very minute grains. In the course 

 of the night these disappear, so that testing a leaf with 

 iodine 1 shortly before daylight usually gives no result. A 

 leaf cut off from the stem before nightfall, however, responds 

 readily to the iodine test for starch in the morning. This, of 

 course, shows that the starch made during the day remained 

 in the leaf cells, where it was formed. It is very generally 

 true that starch carried from any part of the plant to an- 

 other part is first changed to sugar and travels in the form 



1 This turns starch grains blue or almost black. 



FIG. 28. Starch from root- 

 stock of canna 



Magnified 300 diameters 



