Storage Stems. 47 



out any order in the arrangement of the eyes ? Where are 

 they most numerous ? What do you think the eyes are ? 

 Do you know what they will do if the potato is planted ? 

 Do they ever grow if it is not planted? If stems grow from 

 the eyes, the eyes are buds. Normal buds should have leaves 

 below them. Find the rudiment of a leaf the eyebrow. 

 Buds are the outgrowth of stems. Potatoes, then, are 

 homologous with stems. Such underground stems are 

 called tubers. Cut the potato in two crosswise through the 

 center of an eye. Put one piece, cut side down, on 

 a plate, and pour around it a spoon- 

 ful of ink. (Red ink if you have it. 

 Several pupils can use one plate.) 

 Cut a very thin slice from the other 

 piece and hold it up to the light. 

 Draw the section. Make a section 

 through another eye. Does the line 

 in this also run to the eye? We Fig - 30 ' Section of a potato - 

 have learned that stems are made up of bark, wood, and 

 pith. In our experiments with ink only the wood absorbed 

 ink readily. What do you think is inside the line ? What 

 between it and the skin ? Now, see what the piece in the 

 ink says about it. First cut off a very thin slice, then 

 another, which you examine. What part of a potato has 

 wood fibers ? Did you ever see this thin layer of wood 

 conspicuous in a boiled potato ? Evidently only the outer 

 layer of bark is the skin. A potato, then, is a stem almost 

 entirely made up of pith and inner bark. These parts are 



