244 University of California Publications. [Botany 



directly in water for a few minutes. On removing the slide and 

 wiping off the superfluous water, a cover glass is placed over the 

 material, and with slight pressure and with a rolling motion, the 

 plants are broken apart and the cells fall down on their flat sur- 

 faces. The cover glass should be removed by sliding it to one 

 side, and not by raising it straight up. This helps to spread the 

 cells out in a thin layer, and assists in getting them to adhere to 

 the slide. A little albumin fixative may first be placed on the slide. 



Picric acid will bring about the same results as alcohol, and 

 is a good killing agent, but has many disadvantages. Too much 

 time is required to kill the plants, and then much more time is 

 required to get rid of the acid. This is done by washing in alco- 

 hol, and care is necessary to prevent the shrinkage of material. 

 Picric acid also has a tendency to loosen the plants from the slide, 

 which then become lost in washing, and, further, it has the disad- 

 vantage of not being a killing agent that can be followed by the 

 best differential nuclear stains. 



The very best preparation I have thus far found for causing 

 the cells to separate is a strong solution of iodine in strong aque- 

 ous solution of potassium iodide. This is an excellent killing 

 agent, acting instantaneously, without shrinking the protoplast 

 to any perceptible degree. Material is mounted on the slide as 

 above described, and a drop of the solution placed upon it, or the 

 whole slide placed in the solution for 10 to 30 minutes, though 

 much longer time will not injure the plants. The material is now 

 washed with 95 per cent, alcohol for about the same length of 

 time, then placed in water for a few minutes, after which it is 

 ready to be treated as above described. The cells break apart 

 readily, adhere to the slide well, and on drying are left round and 

 plump and ready for staining. All of the best differential stains 

 which I have employed for both nucleus and granules may be 

 used after this killing agent with excellent results. 



This method is in many ways superior to the microtome sec- 

 tions. There is far less chance for misinterpretation of the shape 

 and location of various cell-organs. One obtains by this method 

 single cells free from other or parts of other cells, a thing which 

 is practically impossible to obtain with microtome sections. Per- 

 plexity and confusion arise when one attempts to interpret parts 

 of several or even of two cells in an oblique section. 



