and Laboratory Methods. 



2555 



the leaves or stem except at the point of section. Place the tips at once in a 

 glass of water from the aquarium and exhale into the water through a tube several 

 deep breaths. This operation charges the water with an excess of carbon dioxid, 

 which is absorbed by the plant cells. Keep the specimens away from direct 

 sunlight or arc light until ready for use. To mount them, half fill a cell, No. 17 

 is best, with water from the glass and place in it one or two of the tips with their 

 cut ends up and fully submerged, so that the bubbles of oxygen may be seen as 

 they increase in size at the cut end of the stem and become detached and rise to 

 the surface. Focus on the cut end of the stem first, and note the absence of 

 oxygen bubbles, or the slow rate at which they appear. Move the slide on the 

 stage and study the leaf arrangement, form, and cellular structure while the light 

 is acting on the plant. Again focus on the cut end of the stem. To increase 

 the activity of the cells remove the water tank used for cooling the light, so that 

 the full heat power may act. To imitate the conditions of a frost, put a pipette- 

 ful, or less, of ice water in the cell while it is under observation, and note the 

 marked decrease in the evolution of oxygen. Remove some of the water with a 

 pipette and drop into the cell a small sliver of ice, which, if not too small, stops 

 the evolution of oxygen and kills the protoplasm of the cells so that activity can 

 not be renewed. While the ice is melting, convection currents of cold water 

 may be seen falling through the warmer water in the cell. A. H. Cole. 



The Museum. 

 IX. 



THE CASE— Continued. 



Relief maps, geological features, as mud flowage, tracks, ripple marks, etc., 

 can be framed in low, flat cases on legs, glass tops and sides (Fig. 68), or simply 

 framed, face exposed, and fastened to walls, or left on the floor on rollers (Fig. 



Fig. ('(8. — Relief map in floor case on legs. 



69), or placed on wooden pedestals. The material for all cases should be wood 

 in the frames ; black walnut, ash, chestnut, oak, or mahogany, or, in case of nee- 



