1891.] MICROSCOPICAL JOURNAL. 53 



is a circular disc upon the centre of which are ruled two sets of ten 

 lines, at right angles to each other, the lines being five-tenths milli- 

 meter apart. The lines are very neatly ruled and covered by a thin 

 cover-glass cemented to it with balsam. 



It is apparent that the system has a wide application so far as the 

 magnifications to be attained are concerned. The equation giving the 

 magnification is : 



b 



x= ~ X c. 



a 



a being the length of object, b the length of image, c the ratio of 

 the image to the drawn figure. 



Suppose that the amplification of objective is 5 X ; that the lines on 

 the eye-piece slide be one-half millimeter apart, and those on the 

 cardboard be 6 millimeters, then a: = 5 X 6 X 2, or 60, for the unit of 

 the card squares are twice those of the eye-piece squares. 



To use a series of objectives, or of squares for the eye-piece and for 

 the cardboard are easy matters. A single glass ruled to half millimeters 

 made to fit a low-power eye-piece is suflicient to try the plan. Card- 

 boards, either of Bristol board or heavy-calendered manilla paper, may 

 be ruled into squares 3, 5, or 7 millimeters, etc., until the student has 

 all the combinations desirable. 



By adopting this plan of drawing figures, I have found that objec- 

 tions which I find to using the camera are avoided. The lighting is 

 not interfered with, the image moves but little, if any, with the move- 

 ment of the head, and the image can not be distorted. It is true that 

 the accuracy of the figure depends on the skill of the artist, but a short 

 trial of the method will satisfy most students that the actual variation of 

 the drawing in symmetry from the image is less than that in figures 

 made by the camera. 



The objection now existing that American makers have not on hand 

 necessary slides will be gladly removed by them as soon as they see a 

 demand. 



Sixteenth Annual Report of the American Postal Microscopical 



Cluh. 



By R. H. ward, M. D., 



TROY, N. Y. 



\^Contintied from ^age jj.] 



Botany. 



Corn Silk and Pollen. — Early in the morning before sunrise pollen 

 was sprinkled upon a silk just protruding from the shuck ; after five or 

 six hours the ends of the silk were cut oft', put into camphor v/ater, and 

 after several days mounted in the same. By focussing up and down the 

 pollen tubes may be seen. The pollen must be sprinkled on &. fresh 

 silk early in the morning while it is damp. If no tassel can be found 

 ready to shed its pollen, cut oft' one and hang it in the sun ; in half an 

 hour or more it will fall copiously. In four or five hours hundreds 

 of tubes will be found penetrating each silk. If the silk thus specially 

 fertilized be mounted in some suitable medium (water will answer) and 



