462 MANUAL OF BOTANY 



meshes of their substance, they break down to a certain extent, 

 splitting off a quantity of starch which is poured out by the 

 leucoplasts or deposited in their interior by the ohloroplasts, 

 leading to the appearances already described. The formation 

 of starch is thus a secretion by the plastid, just as that of 

 cellulose is a secretion by the protoplasm of the cell. In those 

 cases where small grains of starch are formed without the inter- 

 vention of a plastid, the work is done by the protoplasm of the 

 oeU. 



The most recent researches render it highly probable that 

 the formation of aleurone grains is precisely similar in the way 

 in which it is brought about. 



The formation of fat is due to similar behaviour on the 

 part of the protoplasm. It can be observed most easily in the 

 case of certain Fungi, when they are not well nourished. The 

 protoplasm is found to get less in amount, the vacuolation 

 becomes very considerable, and the cavities are found to contain 

 large drops of oil. The elaioplasts to which reference has 

 been made behave similarly, their substance diminishing at 

 the same time that fat or oil makes its appearance. The de- 

 composition of the protoplasm is here not accompanied by 

 much reconstruction, so that it is soon very greatly diminished 

 in amount, while the fat, the product of the catabolic processes, 

 increases. 



The formation of the enzymes described in the last chapter is 

 another instance of the same kind. These are gradually 

 elaborated by the protoplasm from its own substance, their 

 development being attended by the formation of granules much 

 as is that of cellulose. 



One of the most important of these secretions is the green 

 colouring matter, ChloropJiyll, which we have already seen is 

 present in the form of a solution in the meshes of the ohloro- 

 plasts. The formation of chlorophyll is a more specialised pro- 

 cess than any of those which we have just been considering, 

 and is dependent upon a variety of conditions. It probably 

 involves not only the self-decomposition of the protoplasm, but 

 also other processes taking place in its meshes. 



The conditions necessary for the formation of chloro- 

 phyll are, 1st, access of light, 2nd, a particular range of tempera- 

 ture, 3rd, the presence of a minute quantity of iron in the 

 plant. If a plant be cultivated from seed in darkness, the re- 

 sulting seedling will not be green, but will have a yellowish- 

 white colour. When examined by a microscope the plastids 



