PECAN ROSETTE. 7 



tiguous to a diseased branch, showing that external signs may be 

 preceded by deep functional disturbances. Conditions unfavorable 

 to growth tend to intensify the signs of yellows but do not cause 

 the disease (71). Yellows is transmitted by budding or grafting 

 from diseased trees to healthy stock, and infections through the 

 roots as well as the stems may take place in this way. However, all 

 attempts to infect with the expressed plant juices have thus far 

 failed, nor have insect relations been discovered. 



Peach rosette (70, 72) and little peach (73) differ in the charac- 

 ter and sequence of the signs, but are similar in type to peach yel- 

 lows. All three diseases induce deep changes in assimilation, trans- 

 location, structure, and development. All may appear first in one 

 branch, and they are transmitted by budding or grafting. The dis- 

 ease progresses gradually from the point of infection, requiring 

 longer for the development of external signs in the top when infected 

 by root grafting than when grafted into the branches. That rosette 

 may not affect the whole tree at once was shown in one case where 

 buds from branches showing external signs transmitted the disease, 

 whereas those from the apparently healthy side failed to give infec- 

 tion. The normal side of this tree, however, developed rosette the 

 following season. The outer leaves of rosettes fall early. 



In spike disease of the parasitic sandalwood we find a close re- 

 semblance to the peach-yellows group. The spikelike appearance of 

 the leaves standing out stiffly from the branches suggested the name 

 "spike disease." The entire tree is not attacked at once over the 

 whole top, but symptoms appear first on one, then on several branches, 

 and gradually spread over the tree. The internodes become short- 

 ened and the leaves reduced in size and narrowed; The continuous 

 development of buds into new leaves and branches throughout the 

 year produces a growth closely resembling the " witches'-brooms " of 

 the peach, and with the progress of the disease the leaves become 

 smaller and more chlorotic. No blossoms or fruit are borne in the 

 later stages, though sometimes flowers and fully developed fruit are 

 formed on portions of trees still retaining their normal appearance. 

 Death of the haustoria and fine root ends keeps pace with the prog- 

 ress of the disease. 



Spiked leaves and branches contain a marked accumulation of 

 starch (24) . In the diseased leaves this starch is distributed through- 

 out the parenchyma, especially in the sheaths of the fibrovascular 

 bundles, and no marked difference in quantity is found at different 

 periods of the day. In the diseased twigs the starch occurs as grains 

 of considerable size in the pith, in the medullary rays, in the wood, 

 and in the bast fibers; whereas in the normal twig such grains are 

 rarely found except when the leaves are fully matured. This accumu- 

 lation in the twigs precedes external signs of the spike disease both 



