PECAN ROSETTE. 13 
The spongy parenchyma of these parts is also more compact, and 
the intercellular spaces are smaller than in the green areas. The 
chloroplastids are decidedly smaller and often are pressed so closely 
against the cell wall as to be almost invisible. In the fruit the 
structural derangements are similar in general to those occurring in 
the diseased leaves. 
Dilutions of the virus up to 1 to 1,000 were found to be just as 
potent as the undiluted juice expressed from diseased plants, but at 
dilutions greater than 1 to 10,000 no infections took place. Where 
infections took place with the higher dilutions, the incubation period 
was no longer than when undiluted juice was used, thus showing a 
rapid reproduction of the virus within the plants. This virus was 
found to be entirely removed by passage of the expressed juices 
through porcelain filters of the finer grades (29). 
Taubenhaus (76) reported experiments in which mosaic of sweet 
peas was transmitted by insects and by needle inoculations with plant 
juices. 
Reddick and Stewart (63, 64, 75) found mosaic of beans trans- 
missible by rubbing the young leaves of normal seedlings with 
crushed leaves from mosaic plants and obtained a high percentage 
of mosaic by sowing seeds from diseased plants. In cases of inocu- 
lation external signs usually appeared after about four weeks. 
Many other chlorotic diseases such as aster yellows, cassava leaf- 
curl, mulberry dwarf, cotton leaf-curl, little-leaf of the vine, citrus 
mottle-leaf, raspberry leaf -curl, apple rosette, and mosaics of peony 
and sweet potato present characters suggesting a possible relation to 
the group of infectious diseases. However, they have scarcely re- 
ceived sufficient study for any final statements regarding infectivity 
or 'causes. With this brief general review the particular disease 
under investigation may now be considered. 
STUDIES OF PECAN ROSETTE. 
RESULTS OF PREVIOUS WORK. 
Pecan rosette was recognized by orchardists as far back as 1900, 
but no early published references to the disease have been found. 
Field investigations by W. A. Orton were undertaken in 1902 and 
continued about four years. During the years 1910 to 1913 field 
studies were carried out independently by the writer. The results 
of these two sets of field studies were brought together and published 
as a joint paper (56). With the exception of a few brief references 
to the*disease, this was the first published account of pecan rosette. 
The disease is fairly well distributed over the pecan-growing 
regions of the Southern States, but has not been reported from the 
northern limits of pecan culture. 
