EQUIPMENT OF THE LABORATORY. 



95 



There should be hot-water pipes, cold-water pipes, steam pipes, a steam 

 bath, gas-pipes, compressed-air pipes, exhaust-air pipes (plate 10 and fig. 81), and 

 electrical wires for light and motive force. There should be thermostats, water- 

 baths, cooled rooms, ice-boxes, steamers, dry-ovens, autoclaves, a distilled-water 

 outfit, an alcohol-still (by which waste alcohol may be recovered or absolute alcohol 

 prepared), an ether-still, filters, gas-generators, gas-furnaces, anaerobic apparatus, 

 the very best microscopic outfits including apochromatic lenses, photographic and 

 photomicrographic appliances, liquid-air receptacles, cylinders of compressed carbon 

 dioxide and oxygen, microtomes, paraffin baths, glassware, balances, chemicals, and 

 many minor pieces of apparatus. 



Fig. 80* 



*Fic. 80. Angular leaf-spot of cotton in which stomatal infections appear to be the rule. This 

 leaf represents the secondary stage of a natural infection, i. e., the spots have browned and shriveled, 

 and they involve the entire thickness of the leaf. In an earlier stage of the disease the spots are 

 limited to the under side of the leaf (mesophyll), and occur in the form of small water-soaked, 

 uncollapsed areas surrounding stomata, under which nests of bacteria occur. These spots gradually 

 deepen so as to involve the palisade tissue, and then they become visible on the upper surface of the 

 leaf. The spots are not yet shriveled or browned, but if the leaf is held up and viewed by trans- 

 mitted light they appear as translucent areas, while by reflected light they are dull and wet-looking. 

 A little later they present the appearance shown in this figure. The writer has obtained all stages of 

 this disease in Washington by spraying upon the plants young agar cultures of Bacterium malvace- 

 arum suspended in sterile water. 



