242 THE USE OF THE MICROSCOPE 



the number of over 2,000 in all. Figures showing smooth 

 threads in Lilium, between leptotene stage and diplotene, 

 are taken from too slowly fixed preparations, or from cells 

 touched by anther sap. Also, the pachytene thread in 

 Lilium is not coarsely double except at the brief diplotene 

 stage; and the beaded threads are perfect, ''flakes" or 

 ''knots" being results of slow fixing. In fixing large 

 anthers, such as those of Lilium, it may be best to split 

 them lengthwise between the two pairs of loculi, before 

 putting them in alcohol-acetic-chloroform. 



The writer agrees with Bolles Lee, with regard to the 

 superiority of thin cedar oil as a clearing agent. 



Iron-acetocarmine Temporary Preparations. — With cer- 

 tain precautions, acetocarmine may give rapid fixations. 

 Large anthers should be split lengthwise, and cut across. 

 These cut anthers, after drying with blotting paper, should 

 be put in a drop of iron-acetocarmine, which after two 

 minutes or so is removed with blotting paper, and a new 

 drop added. The pollen mother cells should be pressed out, 

 either by a scalpel, a spear-headed needle, a glass slide, or 

 by slight pressure or tapping on a cover-glass. The anther 

 walls are then removed with a needle, and a cover-glass 

 put on; excess liquid being drawn off with blotting paper. 

 The preparations are sealed as soon as possible with melted 

 paraffin, applied with a piece of hot metal. They are left 

 for some days or weeks to stain fully. Then they are to 

 be examined, preferably with a water-immersion objective. 

 (Slides sometimes keep for months, in the dark.) Any 

 selected cell may be squeezed out at this stage, when the 

 cytoplasm is plastic; and usually cytoplasm and chromo- 

 somes can be freed from the cell as a whole, and flattened. 

 Before this, the cytoplasm may be too liquid, and after 

 some weeks it may be too brittle, to squeeze out. Such 

 flattened groups of chromosomes, adhering to the cover- 

 glass, are well suited for examination with oil-immersion 

 objectives, and for photography. The chromomeres can be 

 seen and counted in rapidly fixed preparations of the pollen 

 mother cells of Lilium and many allied genera, at the pachy- 



