LABORATORY AND TEACITING METHODS 65 1 



of iron in the soil. M. O. Johnson at the Hawaiian Experiment Station has shown 

 that the chlorosis of pineapples occurring on highly manganiferous soils can be cured 

 by spraying the leaves with ferrous sulphate, similarly in Porto Rico the disease due 

 to calcareous soils can be cured by the application of iron salts.' 



LESSON 38 



Study of Mislldoe. — Procure living material of the American mistletoe (Phora- 

 dendron flavescens) or European mistletoe {Viscum album) and make sections with 

 the sliding microtome of the stem of host and the parasitic roots of the parasite 

 and study in detail the association of host and parasite (Figs. 119, 120, 121). 



This method of study can be used with Loranlhus Sadebeckli on Citrus niedica. 

 See Klebahn, Dr. H.: Grundziige der allgemeinen Phytopathologie, 191 2: no. 

 Cf. TuBEUF, C. von: Infektionversuche mit der rotfriictigen Mistel. Naturw. 

 Jahrb. Forst. und Landw., xi: 51; Bot-Centralblatt, 123: 293. 



Dodder. — Gather material of Cuscuta, Orohanche, Gerardia, Lathraa and other 

 parasites, and study their anatomy as connected with the anatomy of the hosts on 

 which they occur (Figs. 117, 122, 123). 



The writer has frequently made sections of the stems of the Jo-Pye weed, Eupa- 

 torimn purpureum, parasitized by Cuscuta Gronovii. These sections were made with 

 the sliding microtome and have been kept in 50 per cent, alcohol until ready for use. 

 As class exercises they have been double-stained with safranin and methyl green, 

 which brings out the relationship of host and parasite very nicely. Finally the 

 sections have been mounted in balsam and drawn by each member of the class. 



LESSON 39 



Wire Worms in Plants. — As the subject of the injurious effects of animals on 

 plants is a large one and belongs rather to entomology and other departments of 

 Zoology only one case will be studied here. 



Nematode Infection of Plants.- — Secure material showing the root infection of 

 horticultural plants by the nematode worm, Heterodera radiciccla. Make sections 

 showing relation of parasite to host. 



Take healthy plants and infect them by transplanting into a soil containing the 

 eggs or the live round worm. Study entry of the parasite into the hosts and by 

 paraffin, celloidin or sliding microtome sections, study the relation of the parasite 

 and host plants. 



Similarly, a study of insect galls can be made and their anatomy studied accord- 

 ing to the description of galls previously given in the second part of this book. 

 Such a study of galls should be encouraged by the teacher, wherever time and the 

 arrangement of the courses makes it practicable to do so. 



^ GiLE, P. L.: Chlorosis of Pineapples Induced by Manganese and Carbonate 

 of Lime. Science, new ser., 44: 856, Dec. 15, 1916. Maze, P., Ruot, M. and 

 Lkmoigne, M.: Calcareous Chlorosis of Green Plants: The Role of Root Excretions 

 in the Absorption of Iron in Calcareous Soils. Compt. Rend. Acad. Sci. (Paris), 

 157 (1913), No. 12, pp. 495-498 (Exper. Sta. Rec. xxix: 826). 



