650 LABORATORY EXERCISES 



LESSON 37 



Enzyme Diseases. — Study these diseases of green plants by taking a series of 

 leaves of various variegated Anthuriums and other greenhouse species and treat 

 them as follows: The leaves to be tested are to be boiled for about one minute in 

 water, when they should be flaccid and free from intercellular air. They are then 

 placed in methylated spirit warmed to 50° to 6o°C. : cold spirit will remove the chloro- 

 phyll, but not so quickly. To produce the iodine reaction, place the decolorized 

 leaves in alcoholic tincture of iodine, dilute with water to the color of dark beer. 

 In a few minutes they will be stained, and after washing in fresh water, they should 

 be spread out on a white plate so that their tint may be well seen. When full of 

 starch they are almost black, and with less amount of starch, the color sinks through 

 purple, gray and greenish-gray to the yellow tint of starchless leaves (Sach's method). 



In Schimper's method prepare strong chloral hydrate by dissolving the crystals 

 in as much distilled water as will just cover them. The solution is now colored by 

 the addition of a little tincture of iodine and is ready for use. 



Discoloration of Cut Pieces of Plants. — Cut slices of fresh potatoes and expose them 

 to the action of the air. Also grate some of the material and test the rapidity of 

 discoloration. 



Take similar pieces and place them in distilled water for twelve hours. Then 

 expose the cut pieces to the air, and note the result. 



These same . experiments can be performed with various toadstools and fleshy 

 fungi, when these are in season. 



Bibliography. — Allard, H. A.: The Mosaic Disease of the Tobacco. Bull. U. S. 

 Dept. Agr., No. 40, pp. 33, Jan. 15, 1914- 



LoEW, O.: Catalase. U. S. Dept. Agr., Report 68. 



Stone, Geo. E. : Mosaic and Allied Diseases with Especial Reference to Tobacco 

 and Tomatoes. 25th Annual Report Mass. Agric. Exper. Sta., 1913: 94-104. 



Woods, A. F.: Mosaic Disease of Tobacco. U. S. Dept. Agr., Bureau of Plant 

 Industry, Bull. 18. 



Chlorosis. — Grow vetches and peas in nutrient solution; add 2 per cent, calcium 

 carbonate, when chlorosis immediately appears, even if iron sulphate is present in 

 the solutions. A few days in iron nitrate will cause the return of the green color. 

 In treating plants for chlorosis, a 0.2 per cent, solution of iron nitrate sprayed on the 

 leaves gives good results. 



Where pineapples can be grown in the greenhouse or the open the following facts 

 will suggest a line of experiments with them and their chlorosis. 



Chlorotic pineapples in Hawaii. occur on acid or neutral soils that average 5.0 

 per cent. Mn304 and 0.5 per cent. CaO. Chlorotic pineapples in Porto Rico occur 

 on soils containing from 2 to 80 per cent, carbonate of lime and no manganese. 

 That the chlorosis in Porto Rico is induced by the carbonate of lime was proved by 

 direct experiment. Soils which normally produced healthy pineapples were made 

 to produce chlorotic plants by the admixture of carbonate of lime from different 

 sources. We may thus speak of one as a manganese-induced chlorosis and the other 

 as a lime-induced chlorosis. The lime chlorosis has been shown to be due to a lack 

 of iron in the plant, caused by the carbonate of lime diminishing the avaflability 



