244: 



THE AMERICAN MONTHLY [October, 



torn of the tube are used. The constriction supports the potato, 

 and the condensation water falls into the reservoir thus formed in 

 the bottom of the culture-tube. 



If the potato medium is to be kept for some time, we find that 

 there is a great change in the form of the potato, due to evapora- 

 tion of water from it. The inoculation surface becomes irregu- 

 larly concave, the thin end becomes dry, and curls, and the prep- 

 aration presents an unsightly appearance. 



When the potato cultures are to be used for exhibition pur- 

 poses, it is desirable to have them present a neat appearance. 

 The aim of the writer is to describe an apparatus which he has 

 devised to prevent the changes in form referred to. 



The apparatus consists of two pieces : a plugger, represented 

 by figure i, and a curved knife, represented by figure 2. 



Jll 



Fig. J. 



rif. z. 



ris.'6 



The plugger is made from a metal tube about six inches long, 

 and of a diameter a little less than the culture-tubes to be used. 

 The side of the metal tube is cut out by sawing slantingly through 

 the wall and across the inner diameter of the tube to the opposite 

 wall at such an angle that the distance traversed by the saw will 

 be about two inches, and then by sawing vertically across the 

 diameter of the tube to the wall of the opposite side. The end of 

 the tube nearest the side opening is sharpened from the outer sur- 

 face, and a wooden handle is fitted into the other end. 



The curved knife (fig. 2) is used to cut a convex surface on 

 the potato section so as to compensate for the loss by shrinkage 

 from evaporation. After a time this convex surface will become 

 nearly flat, whereas, if the surface were cut flat at the outset, it 

 would now be irregularly concave. 



This knife is made by cutting out a segment of a circular tube 

 of about one and one-half inches in diameter, the segment having 

 continuous with it a narrow portion of the wall of the same tube, 



