114 BACTERIAL DISEASES OF PLANTS 



ever. Seedlings and cuttings require only a minimum quantity, 

 but that they must have. A single excessive watering of seed- 

 lings, or cuttings, may destroy your experiment. 



Plants seldom do well if transferred in full leaf to very 

 different conditions as to light, heat and moisture, e.g., from 

 the hothouse to the laboratory or to the garden or vice versa. 



For hothouse experiments great care should be taken to 

 select good soil, i.e., that free from nematodes, ants, and para- 

 sitic soil fungi, such as Rhizoctonia or Fusarium. Often a whole 

 year's work is lost by reason of nematode-infested or fungus- 

 infested soil. If you have any reason to suspect the soil, it 

 must be steamed or baked, or drenched with formalin-water 

 before it is used. Bordeaux mixture sprayed upon the earth 

 will sometimes stop the activities of a damping-off fungus. 



Ants may be kept off benches by having runways all around 

 them and their upright metal supports capped at about 2 feet 

 from the ground by metal cups containing oil in which stand the 

 short legs of the bench. Feed ants sweetened tartar emetic. 



PREPARATION OF SECTIONS 



Free-hand Sections. — Good free-hand sections are very 

 useful in the preliminary examination. They can be made only 

 by one who has enough gumption to sharpen a razor as often as 

 it becomes dull, which is about every day. It is worth while 

 even in a busy semester to learn how to do this. Sometimes 

 a good-natured barber will show you how. The Torrey razor is 

 excellent for section cutting but it is no longer on the market. 



Turgid tissues cut better than flabby ones, which latter 

 sometimes recover turgor if thrown into water. The material 

 to be cut should be held in a cleft of elder pith, never between 

 corks, which dull razors. After a little experience very thin 

 sections can be made of many things; these are usually more or 

 less wedge-shaped, but if they are thin enough to see through 

 that is all that is required, since one seldom mounts for perma- 

 nent preservation anything but microtome sections. 



Microtome Sections. — Read what is said under Apparatus 

 about microtomes. There are several methods of making 



