and Laboratory Methods. 2127 



which were pulsating at nearly normal rate during the exposure of two minutes. 

 To study the opposite side of the worm without remounting it, push the two 

 slides to the edge of the base plate, grasp the ends firmly between thumb and 

 finger, turn the slides over with a quick motion so that little or no liquid will 

 run out, and replace them on the base plate. The advantage of the base plate 

 is that the worm is easily moved about under the objective without any irritation 

 of the animal, and at the same time it acts as a tray to catch any liquid from the 

 slides. 



Five parts of water to one part one per cent, chloretone solution is the mini- 

 mum strength, and in it earthworms live for hours and revive when transferred to a 

 quantity of clear water. Occasionally it is necessary to add a drop of one per 

 cent, chloretone solution to the liquid on a slide to quiet an unusually resistant 

 specimen. After using the worms place them in about a half litre of clear water, 

 and in an hour or less transfer them to the jar of filter paper and about ninety 

 per cent, of them will be alive and active and suitable for use the next day. 



To kill earthworms expanded, place the washed worms in a tray, cover them 

 with water five parts, one per cent, chloretone solution one part, let them stand 

 for a half hour or more and add enough formalin to make the solution about 

 five per cent, strength. A. H. Cole. 



University of Chicago. 



Methods in Plant Physiology. 

 VII. 



CARBON ASSIMILATION— Continued. 



8. Effect of Preventing the Access of Carbon=dioxide to Land Plants. Plant 

 some seeds of clover {TrifoUum pratensc) or of radish {^Raphanus sativus) in each 

 of two small crocks of earth which have previously been heated so as to destroy 

 all animal life. When the seedlings have unfolded their primary leaves, each 

 crock is to be placed in a large wide-mouthed bottle, or under a bell-jar with a 

 tubulature at the top. If a bell-jar is used it must stand upon a ground-glass 

 plate, and have the lower edge smeared with vaseline. The method of preparing 

 one of these jars is shown in Fig. G ; a small open dish containing a strong solu- 

 tion of potassium hydroxid is placed inside with the plants for the purpose of 

 absorbing the carbon dioxid in the jar. The jar is closed with a cork, per- 

 forated for the passage of a glass tube ; all joints are carefully sealed. The air 

 entering the jar is freed from carbon dioxid by its passage through the open 

 U-tube filled with pieces of pumice stone soaked in strong potassium hydroxid 

 interspersed with pieces of solid potassium hydroxid. A control chamber is 

 set up in the same manner, except that the chamber and the ventilating tube 

 have no potassium hydroxid. Place the preparations in strongly diffused (not 

 direct) sunlight; continue the experiment until there is a very noticeable 

 difference in the growth of the two crocks of plants. The plants deprived of 

 carbon dioxid will be found to be deficient in nutrition. 



