384 Colchicine 



ping, brushing, or total immersion oi the phmt in the sokition. The 

 latter method has been used efEectively for root systems and seedlings. 



16B.2: Seed and Seedlings 



One of the most convenient ways to treat plants uses the ger- 

 minating seed placed in solution. The seed may be presoaked or 

 placed directly into the colchicine. Different lots may be removed 

 after given intervals. Then some exposures will not cause doubling; 

 others will prove lethal; and other lots will be at the optimum ex- 

 posure. In this way the most effective concentration and time of ex- 

 posure can be determined by the survival of treated seeds trans- 

 planted alter treatment. Overexposures kill the seedlings, and under- 

 exposure does not lead to new polyploids. 



Plants, when young, are well adapted to treatment. If only the 

 plumule is treated, the roots remain unharmed, and plant growth is 

 not so totally harmed. The growing point may be immersed in col- 

 chicine, or the solution applied to the plant by brush treatment. By 

 sowing seeds in rows, and treating each row with different exposures, 

 the differences between too much treatment and too little will show at 

 the time seedlings are ready for transplanting. Selections for probable 

 polyploids can be made at this time. 



Seedlings of monocotyledonous plants are difficult to treat with 

 colchicine. Special methods'- ^s- 1^. s had to be devised for these cases. 

 Admitting the drug to the growing tissues that lie beneath a coleop- 

 tile sheath has been the chief problem. 



16B.3: Root Systems and Special Structures 



Soaking entire root systems has been effective for many species of 

 the Gramineae.i''- ^^' -^ An alternate period of soaking in colchicine 

 12 hours and in water 12 hours has ^\•orked out with good success. 

 The number of exposures depends upon the particular experiment, 

 material, and concentration. Reference to specific schedules in the 

 literature shows what directions have been most successlul. The 

 technique was developed for sterile species hybrids of grasses and 

 specifically for wheat-rye sterile hybrids to make fertile amphiploids.^"* 



Scales of liliaceous plants,!^ bulbs, corms, and rhizomes represent 

 structures that call for modifications in method. Usually a large mass 

 of meristematic tissues arc present, and unless the whole group of 

 cells responds, the production of mixoploids and chimeras becomes 

 an inevitable result. 



Expanding buds of woody stems require proper timing in order 

 to introduce colchicine when the cells are in their peak of division. 

 In this way mature woody plants can be treated when dormancy is 



