[Cir. 120 — D.] 



LEAF-CUT, OR TOMOSIS, A DISORDER OF COTTON SEEDLINGS.^ 



By O. F. Cook, Bionomist in Charge of Croi) Acclimatization and Adaptation 



Investigations. 



INTRODUCTION. 



Seedlings and young cotton plants are subject to a peculiar disorder 

 .that results in extensive injury to the leaves and frequent abortion 

 of the tenninal bud. While these injuries are seldom fatal, they 

 undoubtedly impede the growth of the plants, delay the period of 

 production, and reduce the crop. Though not taken into account 

 hitherto, the losses occasioned by the leaf-cut disorder, though most 

 severe in the Southwestern States, seem to be very general and must 

 amount to millions of dollars every year. With the advance of the 

 boll weevil this form of injury to the young plants acquires a more 

 serious aspect, because it is of the utmost importance to shorten the 

 period of production in order to avoid damage by the weevil. The 

 leaf-cut handicap can be reduced by improved cultural methods, as 

 stated in previous publications of the Bureau of Plant Industry.- 



LEAF-CUT DISTINGUISHED FROM LEAF-CURL. 



Leaf-cut is suggested as a popular name because mutilations of the 

 leaves are the most characteristic symptom of the disorder. The name 

 '"' juvenile leaf-curl " has been applied in previous publications, but 

 is inconveniently long and not sufficiently distinctive. Moreover, 

 the leaves of cotton seedlings are subject to another malformation, 

 induced by plant lice, for which the name " leaf -curl " is more appro- 

 priate. 



Leaf-cut is very widely distributed and familiar to planters, though 

 generally confused with the leaf-curl caused by plant lice. Though 

 both forms of injury are likely to be found in the same field, or even 

 on the same individual plant, they are easily distinguished. (Fig. 1.) 

 The leaf-curl is a crumpling or arching up of the leaf between the 

 veins, but without perforations or rents. Even in cases of great dis- 

 tortion by leaf-curl the tissues of the leaf are left entire, without 



1 Issued Apr. 5, 1913. 



2 See Report of the Chief of the Bureau of Plant Industry, U. S. Department of Agri- 

 culture, for 1011, p. 24 ; for 1912, p. 27 ; and U. S. Department of Agriculture, Bureau of 

 Plant Industry, Circular 96, p. 13. 



[Cir. 120] 2^ 



