106 



while we survey that side too. Now if the lines are on the sur- 

 face, a grain like a (fig. 73) would look like b when rolled up on 

 its side. If, on the other hand, these rings mark the edges of 

 concentric layers, coats arranged like the coats of an onion, they 

 would be arranged in the edge view of the grain essentially as they 

 are in the side view. As the grains roll over, we see very dis- 

 tinctly the rings are concentric yet ; the starch grain must be com- 

 posed of layers one over the other. 



If we take a little of the starch from the potato and dry it, 

 without the addition of water, at a temperature of perhaps 150°, 

 we shall see a dark point appearing at one end — usually the 

 smaller. This is the nucleus and around it are arranged the con- 

 centric rings already mentioned. It has been described as a little 

 pedicle or stem by which the starch-grain is attached to the cell- 

 wall. This was when it was still thought that the grains budded 

 out from the wall, a theory completely disproven now, by what is 

 known of the development and functions of the wall, as well as by 

 specific observations on the formation of the grains themselves. 

 The nuclei have been described too as holes, passing into the inte- 

 rior from the outside, and admitting the materials from which the 

 successive layers were formed from without inwards. If the de- 

 velopment of the starch-grain were endogenous, there might be 

 some ground for this hole-theory of the nucleus, but it is now well 

 proven that their formation is from within out, or exogenous. 

 There is no easily accessible specimen at this season of the year, 

 to illustrate this, but writers generally refer to ripening corn, 

 where all the stages can sometimes be seen in a single grain. 

 However, we can easily prove with the specimens under examina- 

 tion that the nucleus is neither a little stem nor a canal. If it 

 were either, it would appear, as we roll the grains, sometimes 

 elongated. As we roll the grains over, by inclination of the 

 stage, or pressure from one side, as before, we see no difference in 

 the shape. of the nucleus. It is the same round or angular black 

 spot, occupying the same position from whatever point it is viewed. 

 If we are lucky, we may get a grain up on end, and examine it in 

 the direction of its long diameter. The position of the nucleus 

 and arrangement of the rings remain the same. 



What can we conclude concerning the nature of the nucleus 

 from this? It was indistinctly or not at all visible in the fresh 

 grain ; it beoomes visible on drying, and looks like an air space. 



