222 THE USE OF THE MICROSCOPE 



can be rooted over water. The common triploid hyacinths, 

 Lady Derby, Grand Maitre, Queen of the Pinks, and King 

 of the Blues, can be used. Anthers are to be squeezed 

 out in iron-acetocarmine, till young pollen grains of the right 

 stage are found. These are recognizable by a metaphase 

 plate of chromosomes filling half or more of the pollen grain. 

 (It takes longer for the stain to penetrate the wall of the 

 young pollen grain than that of the pollen mother cell.) 

 A number of smears should be made from different buds, 

 tested, left some time to stain, covered, and set aside for an 

 hour or two. Then those that show many metaphases in the 

 pollen grains may be sealed with melted paraffin. Wait a 

 few days before examining. Use a water-immersion objec- 

 tive (such as Zeiss apochromatic 70 with collar) with yellow- 

 green light. See whether the numbers of extra chromo- 

 somes, short, medium, and long, vary according to the 

 binomial distribution, or not (Belling, Darlington, Lesley). 

 The hyacinth smears of pollen grains may also be fixed in 

 chrom-acetic-formalin and stained with brazilin. 



7. Numbers of Nodes in the Bivalents of Lilium. — 

 Flower buds about 20 millimeters long, or less, will often 

 give the desired stages, in Lilium longiflorum., grown in a 

 cool greenhouse, early in the year. The anthers from a 

 flower may be examined at intervals. Each is to be split 

 lengthwise, cut into two, dried on filter paper, pressed out 

 into a drop of iron-acetocarmine, and left for a time to 

 stain. All anther debris is to be removed. After covering, 

 superfluous fluid is sucked away with blotting paper, and 

 the slide left for a short time before sealing with melted 

 paraffin, so that capillary pressure may flatten the cells. 

 Then the slide is put away for a week. A water-immersion 

 objective, with a correction collar, gives the best images. 

 Chosen cells may be flattened, or the cytoplasm and 

 chromosomes squeezed out, by pressure on the cover with a 

 mounted needle, if the cover-glass is large and thin. The 

 nodes can be counted in the bivalent chromosomes of early, 

 middle, and late diaphase, in cells in which all 12 bivalents 

 are separable. So the difference in the average number of 



