24 Graft- Infectious Disease of Datura 



the numbers in Tables III and VI are not in all cases identical. A 

 correspondence between the percentage of Q. seedlings and the amount 

 of spininess of valves from which they were derived is scarcely evident. 

 We conclude that the percentage of infection of the seed is only 

 very roughly proportionate to the external evidence of the disease on 

 the part of the plant from which they were derived and that the 

 correspondence largely if not entirely disappears in reference to the 

 divisions of individual capsules. In other words, if a capsule from 

 a plant Avhich is becoming Q. is fully armed and thereby shows no 

 external evidence of infection, its seedlings are relatively low in Q.'s. 

 On the other hand, if the capsule shows evidence of reduction of spines 

 recognized by the grades employed, the seedlings are relatively high in 

 Q.'s. So long as the capsule appears to be infected at all, the grade of 

 spining has no close relation to the percentage of Q.'s in its offspring. 



(c) Inheritance of Q. through Male Gametes. 



It has been shown that the Q. infection is strongly transmitted 

 through the female gametes. The question arises as to whether it can 

 be carried by the pollen. A difficulty lies in the fact that typical 

 Q. plants are devoid of pollen. Occasionally, however, as a plant be- 

 comes infected in the field, some of the flowers may not be so strongly 

 affected as the rest and in consequence may produce a varying amount 

 of pollen. This was the case with five flowers of plant A already dis- 

 cussed. Table VII (p. 34) shows the proportion of Q. and normal offspring 

 when the infection is carried by the male gametes. The pollen from 

 flowers J. 11, A 12 and A 15 was only slightly potent in transmitting 

 the disease, as might be expected from the grade of their capsules, while 

 the flowers A 7 and A x were more active. Unfortunately the record 

 on flower Ax \^ not complete. It is evident that these flowers which 

 throw few Q.'s when selfed do not actively transmit the disease through 

 the pollen, while A 7 transmits the disease actively both when selfed 

 and when the infection is carried through the pollen. The high pro- 

 portion of Q.'s from the self of A 15, the pollen of which was inactive, 

 may have been due to an infection of the pistil which had not yet 

 involved the stamens. Why pedigree 16655 should run so high in 

 Q.'s is not clear unless a single anther of the flower was strongly in- 

 fected and happened to be used in making the cross. It cannot be 

 determined from our present records whether pollen was taken from 

 individual anthers or mixed in making these crosses. 



The experiments show that the male gametes can carry the Q. 



