1894.] MICROSCOPICAL .TOURNAL. 49 



for example Menyanthes. Gases to pass into the organ 

 must traverse a living continuous membrane. This they 

 do by diffusion. 



Intercellular spaces occur in the phleom of the radial 

 bundle. These spaces have large cells lining them, the 

 nuclei of which have an affinity for the side of the cell 

 which borders the air space. This is presumably because 

 the conditions of life are better there. 



Cornell Unhwsity. 



Centering Device for Turn-table. 



By E. E. MAvSTERMAN. 

 nkw london, ohio. 



All turn-tables should be self-centering or have a 

 device for centering which is not mechanical. Centering 

 has become an absolute necessity for neatness where 

 round cells are desired. It is not an easy task if you 

 have no means for centering except the eye. I will give 

 a method for marking the top of a turn table which I 

 have used for some years. Any one can use it, and those 

 who have no centering device are urged to try it. With 

 a little patience and neatness, centering can be nicely 

 done and it will save much valuable time, while it costs 

 nothing. The device will be readily understood by 

 refer ing to the figure and observing the directions. 



DIRECTIONS FOR MARKING THE TABLE. 



1. Draw a diameter in relative position to the clips 

 AA, as in the drawing, p. 50. Be very accurate, so as to 

 have it pass through the center. 



2. Draw several concentric circles near the center as 

 shown in the figure, p. 50. Three is usually enough — one- 

 fourth, one-half and three-fourth inches. These are to 

 be used as guides for the circle or rings which you make 

 upon the slide. The fractional numbers denot the 

 size of covers. (See B in the figure.) 



