30 Graft- Infectious Disease of Datura 



been a strong Q. which, both from competition with more vigorous 

 normal individuals and from the difficulty of securing pollination, might 

 readily be reduced to the production of but a single capsule. A single 

 capsule on a normal plant in the field, however, would be rare under 

 usual cultural conditions. 



To one familiar with the manifestations of the Q. disease, it seems 

 likely that the examples just given above from the literature are in- 

 stances of infected plants rather than cases of blending or of so-called 

 " mosaic " inheritance. The term " mosaic," however, may be applied to 

 the disease, if not to the type of inheritance, since it resembles in many 

 ways the mosaic of the tobacco, beans, and other forms for which a 

 causative organism has not been discovered. 



VII. Discussion. 



Mosaic diseases are not uncommon but their nature is obscure. A 

 number have been described for the Solanaceae (cf. Allard (1)), and the 

 mosaic or calico of tobacco is familiar to all who have grown the plant. 

 The disease of the Jimson described in the present article differs from 

 the others of the family in that it is carried by both seed and pollen and 

 appears not to be transmitted artificially by mere contact or inoculation. 



That grafting communicates the infection to normal plants relates 

 the disease to infectious chlorosis of Ahutilon Thompsoni and other 

 forms investigated by Baur (3). It differs fi'om such instances in that 

 no vegetative function of the plant is obviously impaired. The strong 

 Q.'s, which come from infected seed, although smaller than the normals, 

 are as vigorous as many of the mutants. It also differs from infectious 

 chlorosis of the mallows in that it is carried by seed. 



The profound morphological changes brought about in the leaves 

 and especially in the flowers and fruit are such that Q. individuals would 

 be considered worthy of specific if not of generic separation if 100 % 

 of the seedlings instead of only 79 % came true to the Q. complex. As 

 the facts stand, however, there is much in the behaviour of Q. plants 

 which suggests genetic phenomena. 



