UNITED STATES DEPARTMENT OF AGRICULTURE 



Mfe BULLETIN No. 1038 |Mb 



n^<^>fiw^ Contribution from the Bureau of Plant Indastrv JailkSiii^l^ 



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/ 



By Feedekick V. Rand, Pathologist, Lahoratory 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).^ 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 (17). 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. 



2 The serial numbers in parentheses refer to " Literature cited " at the end of this 

 bulletin. 



76289—22 1 



