256 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



outset to the methods employed. The particular point of 

 technique which demands the most care in dealing with plant 

 cells is fixation. The artifact caused by many fixing agents 

 cannot be too carefully guarded against; it was deemed ad- 

 visable therefore to test each fixative by observing its effect 

 on living cells. This was accomplished by teasing out the liv- 

 ing cells on the slide in the liquid expressed from surround- 

 ing tissues, and observing them while irrigation with the 

 fixative was going on. By employing a Zeiss 2 mm. apoch- 

 romat with comp. Oc. 6, 8 and 12, the effect of the fixative 

 on the finer details of structure could be carefully followed. 

 Some of the most highly recommended fixatives were seen 

 to produce profound disturbances in the structure of the 

 cytoplasm and were therefore modified in various ways in 

 hope of better results. The fact that in different stages of 

 development the cell reacts differently necessitated a sepa- 

 rate test for each stage. The principal fixatives used are 

 as follows: — 



1. Flemming's strong chromic-osmic-acetic. 



2. Flemming's strong chromic-osmic-acetic diluted with 



from one to twenty parts of water. 



3. Flemming's strong chromic-osmic-acetic plus from 



one-tenth to one part of glacial acetic. 



4. Flemming's strong chromic-osmic-acetic modified as 



follows: — 



Chromic 7 per cent. 8 c. c. 

 Osmic 2 per cent. 2 c. c. 

 Glacial acetic 0.5 c. c. 



5. Flemming's strong chromic-osmic-acetic with the 



acetic omitted. 



6. Hermann's platinic chloride-acetic-osmic. 



7. The same diluted with from one to twenty parts of 



water. 



8. Iridium chloride i per cent. 



9. Iridium chloride plus i per cent, of glacial acetic. 



10. Iridium chloride .5 per cent. 



11. Iridium chloride .5 per cent, plus i per cent, of 



glacial acetic. 



