A. F. Blakbslbe 31 



VIII. Summary. 



1. A form called Quercina was discovered in the Jimson Weed 

 {Datura Stramonium) occurring spontaneously like a mutation. 



2. Quercina plants are distinguished from normals by greater denta- 

 tion of the leaves, slitting of the corolla, absence of pollen, partial or 

 entire suppression of spines on the capsules, and certain other characters 

 associated with less vigorous growth. 



3. In a single year's test about 1| 7o of the normal plants in the 

 field took on the Quercina character by the last of the season. The 

 Quercina character generally shows itself weakly in a single branch and 

 gradually spreads to all the new growth. 



4. The Quercina complex is transmitted by seed to about 79 "/^ of 

 its offspring when pollinated from normal plants. The remaining 21 "j^ 

 normal offspring do not produce Quercina seedlings in the next gener- 

 ation. 



5. There is a rough correspondence between the strength of Quercina 

 character in the parent and the number of Quercina plants in its 

 offspring. 



6. In plants which were becoming Quercina, pollen was obtained 

 which transmitted the character. 



7. Quercina cions grafted on to normal plants of the Jimson Weed 

 cause the new growth of the stock to take on the appearance of 

 Quercinas. 



8. The cause of the Quercina characters is a disease transmitted by 

 grafting. 



9. Certain other species of the Solanaceae were found to be susceptible 

 to the disease by gi-afting though to a less degree. 



10. It has not been possible to infect plants artificially by rubbing 

 with diseased leaves nor by inoculation of expressed juice from Quercina 

 plants. 



11. Another disease of the Jimson Weed is briefly described which 

 is highly infectious by contact. 



12. Instances in the literature are cited where the same disease 

 apparently has been recorded but mistakenly attributed to a vegetative 

 segregation or " mosaic" inheritance brought about by smooth and spiny 

 varieties in the ancestry. 



