LABouAronr studies of the stem 49 



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

 grown ill a thick forest, more likely to give timber free from knots? 



ExEitcisH XX. Tub Ascent of Sap in the Stem 



Experiments. — In order to trace the course followed bjr 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 tifteen or twenty minutes examine the stem. 

 If it is translucent, like the ISalsani (Imp(itiens'), the course of the 

 eosin water is readily seen without dissection. Xote the branching 

 of the conducting tissue at the nodes. 



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



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

 diagram or diagrams. 



EXEUCISIC XXI. GEOTROnSM 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 

 tlie stem retains this power of reaction to the elfect of gravity at a 

 later date. 



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

 plant — as a young t^uuflower or a young Nasturtium — into a hori- 

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

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

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



Alternative. Experiment lo. — Tiie leafy scapes of the Slieplierd's 

 Purse {Cnpsella Durin-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 iliagrarn of the stem, etc., set it away in a safe place 

 in a liorizontal position until the next day. 



Compare witli the diagram. Ilepresent any new position by dotted 

 lines on the original diagram. 



Write full notes. 



XoTi-; : — The same scape will sliow 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 liecome vertical, place the scape, still in its bottle, so that 

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

 or three incli(is wide. Draw a diagram of the whole arrangement, and 



OUT. Oi' BOT. — 4 



