A MANUAL OF BOTANY 21 



climb ? Is it similar to or different from the forms adopted 

 by twiner or tendril bearer ? The structures on the " ivy " 

 are really air roots and might have been considered in the 

 previous study. 



Draw a portion of the ivy, showing air roots. 



Table. Make a table of all the climbing vines you know, 

 fillincr out headings as follows : 



Woody or Herbaceots 



Climbs How 



CrLTIVATED OR NOT 



4. Modified Stems 

 Tubers 



Potato. Examine the common potato. What is the 

 shape ? Find the point of attachment to the plant portion 

 that bears it. In particular, look at the eyes sunk here and 

 there in the surface and the markings near them. What 

 structures on an ordinary stem do these eyes and markings 

 remind you of ? What bears the potato ; that is, to what is 

 it attached, a root or a stem ? Observe the cluster of eyes 

 opposite the attachment end. What part of the stem may 

 this be considered ? The potato tuber is a stem modified 

 for a special purpose. What is this purpose ? Try the 

 following test : — 



Scrape some potato flesh, mix it with water, and add 

 iodine solution. What does the result show ? 



Draw a potato tuber, naming all the parts. 



Other tubers. Study, if obtainable, other tubers, as arti- 

 chokes, yams, etc. 



Potato continued. To grow potatoes tlie tuber is cut up 

 into pieces, each bearing one or more eyes, and these j^ieces 

 are planted. Name other plants that are propagated in a 

 similar manner by planting stems. This may be called 



