nybom: vegetatively propagated species 259 



presents practical hints for the mutation breeder. The best time for 

 irradiation seems to be September because the bulbs are then easier 

 to handle than earlier in the summer when the new side-bulbs 

 are formed. A suitable dose is said to be 800 r units. Like Jank, 

 de Mol advocates the use of doses low enough to permit a rich forma- 

 tion of new buds and shoots. The material should be propagated by 

 side-bulbs for 4 years in order to obtain all changes in a pure state. 

 The growing conditions should also be modified so as to stimulate the 

 production of new side-bulbs. 



There was a pronounced similarity between the induced muta- 

 tions and those known to occur spontaneously. There was also, in the 

 main, parallel variations in induced and spontaneous mutability 

 among the varieties. Many of the induced changes occurred, however, 

 in varieties in which they were not known before. 



More recently a Swedish plant breeder, Carlsson, at the plant 

 breeding station at Gullaker, Hammenhog, has taken up irradiation 

 experiments with flower bulbs on a comparatively large scale. I 

 believe we have irradiated some 25,000 flower bulbs for him at our 

 cobalt 60-source at Balsgard since 1955. The doses used have been 

 considerably higher than those mentioned by de Mol, namely, 

 between 2,000 and 5,000 r. This difference may to some extent depend 

 on the deviating irradiation conditions, acute X-rays compared with 

 semi-chronic gamma during 5 to 6 days in the open air. 



Carlsson (22) has not yet published any results from his works, 

 most of his material still being in an early stage. He has, however, 

 already isolated a series of different changes and seems convinced 

 that he shall be able to select types among them that ought to become 

 of future value. In addition to the more common color changes, he 

 has found several cases of white-variegated flowers, similar to the 

 "Cordell Hull" sport of Bartigon. He also believes he has obtained 

 giant sports in several varieties, corresponding to "Bartigon Max" 

 out of Bartigon. 



Other Ornamental Plants 



Preliminary results have also been reported from mutation 

 experiments with some other ornamental plants, the best known 

 examples being those with carnations described by Richter and 

 Singleton (91) and by Sagawa and Mehlquist (94, 95). 



Some of these changes, such as reversions from the spontaneous 



