134 THE ELEMENTS OF VEGETABLE HISTOLOGY 



tents and appear as small oval disks of about constant 

 size. Each chloroplast owes its green color to the 

 substance chlorophyll. The chloroplasts are found in 

 the inner tissues of the leaf, being especially numerous 

 in the cells immediately beneath the epidermal mem- 

 brane. The starting point in the formation of a starch 

 grain by the chloroplast is the appearance of a small 

 projection or bud upon the latter. This projection 

 increases in size as the starch substance is deposited 

 around it, and may become much larger than the 

 chloroplast. The newly formed starch grain may 

 or may not become detached from the chloroplast. 

 In daylight the formation of this assimilation starch 

 by the chloroplasts proceeds with great rapidity, and 

 and the starch must be removed from the place of 

 synthesis to make room for further production. Starch 

 is a colloidal or non-dialyzable substance; therefore, 

 before it can pass through the cell membranes of the 

 leaf tissues, it must be converted into a soluble or 

 dialyzable form. Enzymes present in the leaf cells 

 dissolve the newly formed starch, converting it into 

 soluble starch which can dialyze through the cell walls. 

 This soluble starch is transported by the conducting 

 tissues to different parts of the plant where it is used 

 as a nutrient or stored against future needs. 



Frequently the greater part of the soluble starch 

 is stored in well-protected parts of the plant. The 

 soluble starch or glucose transported from the leaves 

 may be stored in the form of reserve starch, inulin, 

 sucrose, glucosides or cellulose. The leucoplasts take 

 part in the formation of storage or reserve starch from 

 the soluble starch, and the process is somewhat similar 

 to that occurring in the formation of assimilation 



