Plate IX. Deformity resulting from colchicine treatment. Seedlings of Cosmos 

 photographed about two weeks from planting. A-A' show seedlings of untreated con- 

 trols; B-B' show seedlings from seeds treated for four days with 0.05 per cent colchicine. 

 Seedlings from treated seeds have swollen stems and poor root development. In conse- 

 qunce, they are often washed out of the soil when the seed pan is watered because of 

 lack of root anchorage. It is these dwarfed and malformed seedlings which produce the 

 tetraploid tissue which in the next generation may give rise to pure-breeding polyploid 

 species due to their containing both diploid and tetraploid tissue. (From Journal of 

 Heredity, vol. 28, p. 397.) 



