LABORATORY AND TEACHING METHODS 649 



7. One end in moist air, the other in sand. 



8. Two ends in wet sphagnum. 



9. One end in wet sphagnum, the other in moist air. 



10. One end in wet sphagnum, the other in wet sand, etc. 



Try wounding the cotyledons oiPhaseolus, Vicia, etc.; also young seedling plants. 

 Use plaster casts to envelope the cut ends. Cf. Tittman: Physiologische Unter- 

 suchungen uber Callusbildung an stecklinger holziger_ Gewachse. Pringsheim 

 Jahrb. fur wissensch. Bot., xxvii: 164, 1895. 



After securing callus under experimental treatment, then cut, stain and mount for 

 microscopic study. See Kuster, Ernst:, Pathologische Pflanzenanatomie, 2d. 

 Edition. 



LESSON 36 



Gas Injuries. — See Exper. Sta. Rec, xxx, 131, February, 1914. 



Take a series of potted plants and introduce into the soil by means of the hole, 

 in the pot bottom different quantities of illuminating gas by means of a rubber tube 

 connected with the gas pipe. Note the effect of the illuminating gas on the health 

 of the plants. Set willow cuttings in water treated and untreated with gas; note 

 the effect. 



Take another set of potted plants and place them beneath bell jars, as follows: 



Plant A beneath a bell jar with a beaker of water containing illuminating gas 

 introduced into the water from the gas pipe. 



Plant B beneath a bell jar into which free gas is conducted by a rubber pipe from 

 the gas jet. Cf. Stone, G. E.: Effects of Illuminating Gas on Vegetation. 25th 

 Annual Report Mass. Agric. Exper. Sta., 1913: 13-28; The Effect on Plant Growth 

 of Saturating a Soil with Carbon Dioxide. Science, new sec. xl: 792, Nov. 27, 1914. 



Smoke Injuries. — See Clevenger, J. F. : Mellon Instit. Bull. No. 7. 



Take a series of potted plants of different species and expose them to smoke 

 conducted to them by means of glass tubes or rubber tubes from the receptacle 

 where the smoke is generated. Study sections of the smoke-injured tissues. 



Tobacco smoke may be tried on tender plants likewise. Consult Bakke, A. L. : 

 The Effect of Smoke and Gases on Vegetation. Iowa Academy Sciences, 1913 

 (xx): 169-188. 



As to smoke injuries, consult also Bakke, A. L.: The Effect of City Smoke on 

 Vegetation. Bull. 145, Agric. Exper. Sta. Iowa State Coll. of Agric. and Mech. Arts, 

 October, 1913. See also Knight, H. I. and Crocker, Wm.: Smoke and Gas Poison- 

 ing. Bot. Gaz., May, 1913: 337-371- 



Acid Injuries. — Treat plants with dilute solutions of various acids and note 

 their effect on the leaves and flowers. The common morning glories, Ipomcea 

 purpurea, are useful for this purpose. 



Raise some morning-glory plants to flower and treat with dilute acids by spray- 

 ing with an atomizer. Cf. Stone, George E.: The Influence of Various Light 

 Intensities and Soil Moisture on the Growth of Cucumbers and their Susceptibility 

 to Burning from Hydrocyanic Acid Gas. 25th Annual Report. Mass. Agric. Exper. 

 Sta., 1913: 29-40. 



