MECHANIC DEVELOPMENT OF PATHOLOGIC TISSUES 407 



WoRTMANN, J.: Zur Kenntnis der Reizbewegungen, Botanische Zeitung, 45: 819, 

 1887. 



Suggestions to Teachers and Students 



The investigation of plant diseases in general is most important and 

 it should be approached from a number of standpoints.^ The teacher is 

 interested in it, because he desires to arrange the subject matter, so that 

 it may be presented in the laboratory and lecture course. The experi- 

 ence of the writer along these lines may be of service to other teachers, 

 and it is given, therefore, with some detail. Living plants should be 

 kept for experimentation along pathologic lines. The best plants for 

 this purpose will be determined by the locality, by their availability, by 

 the ease of their cultivation and by their successful growth in the green- 

 house during the short days of winter. The experiments outlined in the 

 lessons of part IV can be tried upon these plants, such as the influence 

 of chemicals upon growth, the action of illuminating gas on the health of 

 the plant, and the extremely minute, or excessive action of amounts of 

 chemic reagents, for some experiments conducted by Free at Johns Hop- 

 kins University indicate that various plants react in a specific way to 

 extreme dilution of poisonous substances. ^ 



The plants can be wounded in various ways and on different organs. 

 The repair tissue can be studied by sectioning the healed part and stain- 

 ing with appropriate stains. Various infection experiments can be tried 

 with fungi and the lesions produced can be fixed and imbedded in paraf- 

 fin for sectioning, mounting, and for study later under the microscope. 

 The stock of such material for study can be increased materially by 

 collecting galls, insect depredations on plants, examples of callus for- 

 mation from street trees, which have been injured by horses biting off 

 the bark, or by abrasion with wagon wheels. This material, collected 

 from the streets and highways, from the woods and fields, should be 

 fixed and hardened and finally embedded in paraffin for sectioning and 

 microscopic study. These sections should be furnished along with 

 alcoholic, or dried material of the abnormal plant, so that the student 



^ Cf. Shear, C. L.: Mycology in Relation to Phytopathology. Science, new, 

 ser., xli: 479-484, April 2, 1915. 



Smith, E. F.: Plant Pathology. Retrospect and Prospect. Science, new ser. 

 xv: 601-612, April 18, 1902. 



^Free, E. E.: Symptoms of Poisoning by Certain Elements, in Pelargonium 

 and other Plants. Contributions to Plant Physiology, The Johns Hopkins Uni- 

 versity, March 191 7; 195-198. 



