Techniques of Colchicine Treatment 385 



being broken. By grafting the changed sectors, the new polyploids 

 can be propagated.^ Periclinal and sectorial chimeras are frequently 

 pioduced in treating Avoody species. These chimeras may be propa- 

 gated for generations through grafting. Their role in horticulture 

 is being more fully appreciated from a breeding point of view. 



16B.4: Special Techniques for Studying the Action of Colchicine 



Pollen grains that can be used for artificial culturing work serve 

 well for testing the action of colchicine upon mitosis and growth 

 processes. The specific morphology of somatic chromosomes were 

 studied in Polygonatum, and discovery of natural polyploidy was 

 made directly from these observations. Another valuable feature is 

 the small amoimt of chemical that can be tested. Other mitotic 

 poisons soluble in water can be adapted for testing ^vith the pollen 

 tube methods. 



Several modifications have been made in pollen tube studies since 

 the original paper was published in 1931 by Trankowsky. The par- 

 ticular conditions for an experiment must be worked out and fol- 

 lowed thereafter. In pollen tube studies the detail is not as im- 

 portant as a routine which, once successful for an operation, is always 

 done in that way.*' 



Mitosis in the cells of staminal hairs of Tradescantia can be studied 

 in vivo. Single cells may be followed through the stages of mitosis. 

 When such cells are growing in agar containing colchicine, the total 

 time required for a c-mitosis can be measured. Special chambers for 

 keeping the cells alive for long periods were designed for these studies. 

 While the general technique for observing mitosis in the living cell 

 of Tradescantia has been known for many years, the adaptations for 

 experimental cytology are new.'^-^ 



Colchicine was used so effectively with root tips of Allium ccpa 

 that the test has become known as a method for experimental work, 

 the Allium cepa test. Threshold concentrations in relation to solu- 

 bility are some of the contributions from this method. Standardiza- 

 tion of procedures have been devised so that a variety of chemicals 

 can be measured for properties of mitotic inhibition or chromosomal 

 breakage. The time for exposure, for recovery, and for fixation after 

 treatment are important parts of the routine method. 



Allowing roots to germinate when suspended over a test solution 

 is a modification of the Allium cepa method, and more specifically 

 known as the onion root germination test. 



Tissue cidtures for excised roots, virus tumor tissue, proliferating 

 cells, and regenerative tissues generally may be adapted for the use of 

 colchicine. In vitro and in vivo studies are made by these methods. 



