343 



less dense. It is often said that starch is especially formed in the 

 presence of chlorophyl or the green coloring matter of plants. 

 But we notice that it is generally deposited where there is no 

 chlorophyl, as in the roots, underground stems, the albumen of 



rophyl present or not. When the latter is present, its tendency 

 to collect around the solid matters of the cell, the walls, for in- 

 stance, will lead it to collect about the forming starch-grain, and 

 thus give that grain the appearance of being embedded in chloro- 

 phyl. an appearance often noted. 



The form and appearance of the grains differ for each species. 

 In nearly allied species they are much alike; in distant species, 

 very different. Whether in all or most cases specific characters 

 can be drawn from the grains is not fairly settled. It lias never 

 been systematically studied, so far as I know. In a few limited 

 cases it has been done and with success. From these it is a fair 

 presumption that specific differences in the grains exist, but are 

 hard to recognize on account of their minuteness. 



The size varies much but is tolerably constant for the same spe- 

 cies in mature grains. The smallest measured by the writer were 

 only 2 tt.i in length. They were from the rhizome of Hydrastis 

 Canadensis L. Those measured were the largest grains. On the 

 other hand the grains of potato-starch sometimes reach a length 

 of nearly 50 tt. They are then so large that they can be distin- 

 guished by the naked eye. lit c i n Fig. we. 



1. Bean-starch (Fig. 15G). The grab 

 are in the cotyledons. They are packed ^^^e«!^tS^^^ 



in very closely with aleurone. They are 



of an ellipsoid or reniform shape, and are 30 tt. or less in length. 

 The rings are usually not visible, though sometimes very evident. 

 The nucleus is long and slit-shaped. In two of the grains figured, 

 smaller cracks can be seen. They are caused by heating. They 

 are easily seen by making a thin section of a bean or by simply 



