UNITED STATES DEPARTMENT OF AGRICULTURE 
SyJ&^&fL 
ft BULLETIN No. 1038 
Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 
Washington, D. C. 
March 20, 1922 
PECAN ROSETTE: ITS HISTOLOGY, CYTOLOGY, 
AND RELATION TO OTHER CHLOROTIC DIS- 
EASES. 1 
By Frederick V. Rand, Pathologist, Laboratory of Plant Pathology. 
CONTENTS. 
Page. 
Types of chlorotic plant diseases 1 
Chloroses due to soil or atmospheric 
conditions , 2 
Infectious chloroses 6 
Studies of pecan rosette 13 
Results of previous work 13 
External signs of rosette 17 
Page. 
Studies of pecan rosette — Continued. 
Histological and cytological 
studies 19 
Subsidiary experiments 30 
Probable nature of pecan rosette 31 
Summary , 36 
Literature cited 37 
TYPES OF CHLOROTIC PLANT DISEASES. 
The chlorotic group of plant diseases to which pecan rosette be- 
longs has long been recognized and has presented to the investigator 
some of the most baffling problems in plant pathology. The potato- 
mosaic group began to assume alarming proportions in the British 
Isles and on the Continent toward the end of the eighteenth century 
and at the beginning of the nineteenth century (27, 45, 59 ). 2 Peach 
yellows was known and much written about in the United States 
near the beginning of the nineteenth century (69). Tobacco mosaic 
was first described by Mayer in 1886 (52), but more fully treated by 
Beijerinck in 1898 (IT). Other well-known chloroses will readily 
come to mind in addition to those recently discovered or not so 
generally recognized. 
It is not the purpose of this paper to consider in detail all types 
of plant variegation. Chloroses have to do with the reduction or 
1 The present study was largely carried out under the direction of Dr. R. A. Harper, of 
Columbia University, and was completed under the direction of Dr. Erwin F. Smith, of 
the Laboratory of Plant Pathology, Bureau of Plant Industry. 
3 The serial numbers in parentheses refer to " Literature cited " at the end of this 
bulletin. 
76289—22 1 
