122 Botanical Microtechnique 



is a daily periodicity in die rate of mitotic activity, a periodicity that 

 is characteristic for each species. In order to have many mitotic figures 

 on tlie slides, root tips should be collected at periods when many cells 

 are dividing. 



Bulbs of Allium cepa, Hyacinthus, Crocus, Tulipa, and to a lesser 

 extent of Liliinu are good sources of root-tip material. The following 

 suggestions, based on onion, will furnish the basis for other related 

 subjects. The simplest method of sprouting the bulbs is in individual 

 containers of water, using a tall narrow bottle, jar, or drinking glass 

 of such diameter that the lower third of the bulb is submerged. 

 Change the water twice a day. Bulbs sprout well in moist, steam- 

 sterilized sphagnum. The peaks of mitotic activity for onion are 

 from 1:00 to 2:00 p.m. and 11:00 p.m. to midnight. 



Onion root tips are preserved satisfactorily in fluids of the Na- 

 waschin type; one of the most consistently satisfactory is III. The 

 comparatively expensive butyl alcohol and dioxan methods give good 

 results, but a closely graded acetone-xylene series and careful infil- 

 tration yield excellent preparations for general class use. Bouin's 

 solution yields excellent mitotic figures, especially prophases and 

 telophases. Occasional lots killed with Bouin are extremel) poor. 

 Fluids containing osmic acid are favored by some workers for critical 

 cytological work, but the use of this expensive reagent is not justified 

 for routine work. The formula must be adapted to the plant being 

 studied, and the reader who wishes to use such fluids nuist consult 

 the research literature for details. 



Safranin-fast green and the triple stain give the most complete 

 picture of the entire cell, dillerentiating the cell wall, the texture of 

 the cytoplasm, the achromatic figure, and nuclear structure. Iron 

 hematoxylin stains chromatin an opaque, contrasty blue-black against 

 a gray cytoplasm. Gentian violet-iodine gives a brilliant blue-black 

 translucent chromatin on a perfectly colorless, almost in\isiblc back- 

 ground. Select the stain combination that gives the desired elfcct. 



Hyacinthus and Narcissus also are suiiablc soukcs oi root-tip 

 prcjjarations. The iiutliods are essentially as given for tlie onion. 

 Gladiolus has very small ( hiomosomes, and preparations are of \alue 

 mainly to illustrate (omparatixc chromosome sizes. The possibdities 

 of the numerous kinds ol l)iilb,s, corms. and rhi/omcs available in 

 Ik 1(1 and garden have been l)v no means fully explored. 



Root lips of corn are obtainable by sprouting kernels in a moist 

 chaml)er. When seminal roots and some lateral roots have develoj)ed, 

 cut oil tin nui istem:iii( tii)s. Root tijjs also may be obtained from 



