LABORATORY STUDIES OF THE STEM 49 



nature and origin of the knot. Are trees grown in the open, or those 

 grown in a thick forest, more likely to give timber free from knots V 



Exercise XX. The Ascent of Sap ix the Stem 



Experiments. — In order to trace the course followed by the sap 

 current as it passes from the root to the leaves, make use of water 

 tinged with eosin. Put the cut end of the given (leafy) stem in the 

 colored water. After fifteen or twenty minutes examine the stem. 

 If it is translucent, like the Balsam (Impatiens), the course of the 

 eosin water is readily seen without dissection. Note the branching 

 of the conducting tissue at the nodes. 



If the path of the coloring fluid is not seen from without, dissect. 



Having determined the facts, write a statement, and illustrate by a 

 diagram or diagrams. 



Exercise XXI. Geotropism of the Stem 



The manner in which the growing plumule behaves toward the 

 attraction of gravitation has been seen. It is well to find out whether 

 the stem retains this power of reaction to the effect of gravity at a 

 later date. 



Experiment 9. — This may be done by turning an upright potted 

 plant — as a young Sunflower or a young Xasturtium — into a hori- 

 zontal position, pot and all. Make a diagram of pot, stem, and one or 

 two selected leaves. Leave for a day. Then compare with the diagram. 

 Indicate any changes by making dotted lines for the new positions. 



Alternative. Experiment 10. — The leafy scapes of the Shepherd's 

 Purse (Cnpsella Bursa-pastoris), not too old, make excellent subjects for 

 this experiment. Fit the scape into a small bottle by splitting and 

 grooving the cork. Fill the bottle quite full of water before inserting 

 the scape and cork. Fix the bottle to a block with a rubber band, to 

 keep the bottle from rolling when the arrangement is laid on its side. 

 After making a diagram of the stem, etc., set it away in a safe place 

 in a horizontal position until the next day. 



Compare with the diagram. Represent any new position by dotted 

 lines on the original diagram. 



Write full notes. 



Xote : — The same scape will show the reaction of the stem to light 

 in a marked manner, at least if taken while still freely growing. 

 When the reaction to gravity is completely apparent, and the end of 

 the scape has become vertical, place the scape, still in its l)ottle, so that 

 it faces a window. In front and shading it place an opaque object two 

 or three inches wide. Draw a diagram of the whole arrangement, and 



OUT. OF BOX. — 4 



