Spermatophytes A ngiosperms 263 



Soak beans in water for several hours, and then plant them about 

 an inch deep in loose, moist sawdust. The primary root will be 

 long enough in 2 or 3 days. The large, flat beans are best. Vicia 

 Faba is very favorable. The root-tips of Tradescantia virginica, 

 Iris versicolor, Podyphijllum peltatum, Arisaema tryphylhim, Cypri- 

 pedium pubescens, and many others furnish excellent material. 



Doubtless cell division does not proceed with equal rapidity 

 at all hours of the day. Kellicott 1 has shown that in the root- 

 tips of Alii urn- there are in each 24 hours two periods at which 

 cell division is at the maximum, and two at which it is at 

 the minimum. The maximum periods are shortly before midnight 

 (11 :00 P.M.), and shortly after noon (1 :00 P.M.). The minima, when 

 cell division is at the lowest ebb, occur about 7 :00 A.M. and 3 :00 P.M. 

 When cell division is most vigorous, there is little elongation, and 

 when cell division is at the minimum, cell elongation is at the maxi- 

 mum. Consequently, root-tips of Allium should be collected about 

 1:00 P.M. or 11: 00 P.M. 



We have not made any systematic series of experiments to test 

 Kellicott 's results, but miscellaneous observations seem to indicate 

 that his claim holds good for root-tips. It is certain, however, that 

 abundant mitoses may be found at other times even at 3:00 P.M.- 

 in sporangia of ferns, in anthers of angiosperms, in endosperm, and 

 in free nucleus stages of the embryo of gymnosperms. 



Mitotic figures play such an important part in the development 

 of the plant and in modern theories of heredity, that it is worth while 

 to acquire a critical technic in fixing and staining these structures. 

 Use the various fixing agents Flemming's weaker solution, chromo- 

 acetic acid with or without a little osmic, Bencla's fluid, Bouin's 

 fluid, corrosive sublimate with acetic acid, and any others. Make 

 yourself master of Haidenhain's iron-alum haematoxylin; then add 

 the safranin, gentian-violet, orange combination; then safranin and 

 anilin blue; and then experiment for yourself, but remember that the 

 triumphs of modern cytology have been won with iron-haematoxylin 

 and that you cannot read intelligently the literature of the past two 



1 Kellicott, W. E., "The Daily Periodicity of Cell Division and of Elongation in the 

 Root Of Allium," Bull. Torrey Bot. Club 31:529-550, 1904. 



