CHAPTER IV. THE STEM 

 I. FORMS AND GROWTH OF STEMS 



MATERIAL. Vigorous young hop or bean seedlings grown in pots ; 

 a fresh dandelion stalk ; a stem of pea, squash, cucumber, grape, or passion 

 flower vine, with tendrils. 



APPLIANCES. A bowl of fresh water ; rods of different sizes and 

 smoothness for testing the hold of climbers. 



EXPERIMENT 54. To SHOW THE MOVEMENTS OF TWINING STEMS. 

 Raise a young hop or bean seedling in the schoolroom and allow it to grow 

 about two decimeters 8 to 10 inches in length before providing it 

 with a support. Does the stem form any coils? Bring it in contact 

 with a suitable upright support and watch for a day or two. What 

 happens ? Notice whether it starts to coil from right to left or from left ' 

 to right and see if you can coax it to turn in the opposite direction. When 

 it has reached the end of its stake, allow it to grow about five centimeters 

 (two inches, approximately) beyond, and watch the revolution of the tip. 

 Cut a hole through the center of a piece of cardboard about 14 centi- 

 meters (five to six inches) in diameter, slip it over the loose end of the stem, 

 and fasten it to the stake in a horizontal position, with a pin. Note the 

 position of the stem tip at regular intervals and mark on the cardboard ; 

 how long does it take to complete a revolution ? Does it continue to coil, 

 or to coil as readily, after leaving its stake as before ? What would you 

 infer from this as to the effect of contact in stimulating it to coil ? 



Find out by experiment if it can climb well by means of a glass or other 

 smooth rod ; by a fine wire ; a broomstick ; a large, smooth post. See 

 whether it does better on a horizontal or an upright support. 



EXPERIMENT 55. To ILLUSTRATE THE COILING OF STEMS. Run a 

 gathering thread in one side of a narrow strip of muslin and notice how 

 the ruffle thus drawn will curl into a spiral when allowed to dangle from 

 the needle. Can you think of any cause that might act on a stem in the 

 same way ? Suppose, for instance, that one side should grow faster than 

 the other ; what would be the effect ? (54.) 



Split the stem of a fresh dandelion, or other herbaceous scape, longi- 

 tudinally, and immerse it in a pan of fresh water for a few minutes. Notice 

 how the two halves curve outward, or even coil up like the strip of muslin. 

 This is due to the tension caused by the more rapid absorption of the 



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