.1 HUNDRED MK'liOSCOI'K'AL OBJECTS 227 



first clivision scciiis to be proved by the total of th(; two 

 first anaphase or second metaphase groups being apparently 

 3n, that is, 33. This is also shown by the equality of the 

 two groups resulting from each second anaphase. Make 

 preparations from root tips fixed in chrom-acetic-formalin, 

 run through the alcohols without washing, cut in paraffin, 

 washed in alcohol for some days, and stained with 

 iron-haematoxylin in 70 per cent alcohol, or iodine gen- 

 tian-violet (J. Clausen, 1926). Covers should be 0.17 

 millimeter thick. See if the total number of somatic chro- 

 mosomes is 33. (Belling.) 



22. Chromosomes in a Chain at the Diaphase and 

 Metaphase of the Reduction Division in Rhoeo. — Pollen 

 mother cells at the right stages are to be mounted in iron- 

 acetocarmine, and also as iron-brazilin or iron-hsema- 

 toxylin smears. They stain easily, and too intense staining 

 should be avoided. Covers should be 0.17 millimeter 

 thick. Chains are commonly complete, but are sometimes 

 broken. Complete cii'cles are sometimes found. Biva- 

 lents have not been seen by the writer. (Fresh Rhoeo 

 plants can be grown from seed every year.) (Sands, 

 Belling, Darlington.) 



23. Chromosomes in Circles and Chains in Oenothera. — 

 Iron-acetocarmine is commonly useless for study of the 

 chromosomes, which are wholly, or nearly quite, obscured 

 by granules. But one anther from each flower may be 

 squeezed out in acetocarmine, and will show whether the 

 stage is much too early or much too late. The anthers are 

 cut up on a slide, from two to five tested flowers being used. 

 The smears fix well with chrom-acetic-formalin, and stain 

 excellently with iron-brazilin. If mounted in immersion 

 oil they may be squeezed fiat, and thereby improved. 

 They give clear pictures when viewed with a fluorite 100 

 objective, a pair of 15 (or 12.5) compensating eyepieces, a 

 corrected water-immersion condenser, giving 1.2 to 1.3 

 aperture, Wratten screen No. 57A, and a 3-millimeter 

 diaphragm on the ground glass radiant. (Cleland, Hakans- 

 son, Belling.) 



