Nov. i6. 1914) Pecan Rosette 167 



this experiment nevertheless seems justifiable that whatever the cause of 

 the disease it is not transmissible through the seed (see p. 155). 



Inoculation of tender growing tips with bits of diseased tissue gave 

 negative results. Attempts at isolation of micro-organisms from living 

 rosetted material gave negative results in all cases. Various fungi and 

 bacteria were isolated from partially dead material obtained in four dif- 

 ferent orchards, but no constant form appeared and inoculations gave 

 negative results (see p. 156). These results strongly support the view 

 that pecan rosette is not of a parasitic nature. 



Mycorrhiza have been found promiscuously on both normal and 

 rosetted trees, or perhaps more often the roots of both normal and 

 rosetted trees have appeared to be free from any such fungous growth. 

 It is probable that the disease is not due to the presence or absence of 

 mycorrhiza (see p. 157). 



Where normal buds or cions were worked upon rosetted stocks they 

 have invariably developed the disease during the same or the following 

 season, except in a few cases where the trees used as stock had in the 

 meantime themselves recovered. With few exceptions rosetted buds and 

 cions worked upon apparently normal nursery and orchard trees de- 

 veloped into normal shoots. Where rosetted shoots developed their 

 percentage was no greater than in contiguous nursery rows or orchard 

 trees worked to normal buds or cions (see p. 158). The results here tend 

 to show that rosette is not caused by a perennial fungus mycelium, by 

 bacteria, or by any infecting virus within the tissues of the pecan. 



Healthy nursery trees set in large pots of top soil and of subsoil taken 

 around badly rosetted trees remained normal during the two seasons 

 under observation (see p. 155). This series of tests was carried out in 

 the Department greenhouses at Washington, D. C, small quantities of 

 the soil being used under entirely different environment than present in 

 the location from which obtained. The results are therefore not taken 

 as conclusive, but merely as tending to indicate the nonparasitic nature 

 of the disease. 



Transplanting of healthy nursery trees to holes from which rosetted 

 trees had been removed gave a very high percentage of rosette in the 

 replants, while transplanting badly rosetted trees to situations where 

 less rosette or none at all had been observed gave a very high percentage 

 of recovery (see p. 152). By comparison of the results of these two tests 

 it appears that a soil relation is the important factor in causing rosette 

 rather than any transmission of the disease from one tree to another. 



Thus, from the nontransmission by seed, the negative results of isola- 

 tion and inoculation tests, the varying presence and nonpresence of 

 mycorrhiza, the budding and grafting tests, and the transplanting work, 

 the nonparasitism of pecan rosette is considered a reasonable assumption. 



