CAUSES OF SHEDDING IN COTTON 



Genetic factors indicated, as well as Structural and Environmental causes 



O. F. Cook 

 Bureau of Plant Industry, U. S. Department of Agriculture 



are released from the plant. Any 

 injury to the buds or young bolls, or 

 any external condition that inhibits 

 their development may be a cause of 

 shedding. No doubt the primary 

 causes, those that determine whether 

 abortion is to take place, are genetic 

 and physiological, but the method of 

 shedding has a morphological aspect 

 that needs to be considered, in the 

 interest of a clear understanding of 

 the behavior of different varieties. 



The normal method of shedding is 

 by disarticulation, that is, by un- 

 jointing of the socket where the base 

 of the pedicel is inserted on the fruiting 

 branch. Lloyd's studies show the lack 

 of a structurally specialized abscission 

 layer, and that shedding may result 

 from merely indeterminate divisions 

 and disintegrations of cells, often 

 limited to one or two layers, but this 

 does not justify the general statement, 

 that "the position of the abscission 

 layer is not predetermined by any 

 anatomical relations, but is an expres- 

 sion of a purely physiological phenome- 

 non." On the contrary, it appears 

 that abscission has a very definite 

 morphological position, occurring al- 

 ways at the same place, in the socket or 

 insertion of the pedicel, which is 

 bordered and bounded by the stipular 

 rim.2 



Considering that pedicels represent 

 internodes, the sockets are the articu- 

 lations or nodal points, where un- 

 specialized, embryonic tissues would be 

 expected. The articulation is marked 



^ Lloyd, F. E., "Environmental Changes and their Effect upon Boll-Shedding in Cotton 

 (Gossypium herbaceum)." New York Acad. Sci. 29:1-131, 1920. Since the observations relate 

 entirely to American Upland varieties, the name herbaceum is not applicable. It belongs to cottons 

 of the Asiatic type, which are not cultivated in the United States. The American Upland cottons 

 are referable to Gossypium hirsutum, although some writers place the Texas Big-Boll varieties 

 under Gossypium mexicanum. 



-See Morphology of Cotton Branches, Circular 109, Bureau of Plant Industry, Jan. 4, 1913, 

 p. 13, and Brachysm, A Hereditary Deformity of Cotton and Other Plants, Journ. Agric. Re- 

 search, 3:394, Feb. 15, 1915. On page 13, line 11, of Lloyd's paper the word "internode" probably 

 should read "pedicel," though the meaning would still be doubtful, since there is no reason to 

 suppose that abscission takes place above the base of the pedicel. 



199 



IN VIEW of the recent publication 

 of Professor Lloyd's long-expected 

 contribution,^ and the interest that 

 is likely to be aroused by so extensive a 

 treatment of the subject, attention 

 may be called to additional facts that 

 may affect some of the conclusions. 



Shedding is one of the special terms 

 of cotton culture, referring to a fact 

 of great agricultural importance, that 

 many floral buds and young bolls are 

 blasted and fall off, even when there 

 are no direct injuries by boll weevils 

 or other pests or diseases. Some writers 

 treat shedding itself as a disease, while 

 others consider it a normal habit of the 

 plant to reject superfluous buds or 

 young fruits that could not be brought 

 to maturity. The widely divergent 

 opinions show the need of more infor- 

 mation. 



Shedding is a consequence of abor- 

 tion, and the danger of excessive 

 abortion is to be recognized in the 

 breeding of varieties, as well as in the 

 improvement of cultural methods. The 

 diversity and complexity of the en- 

 vironmental factors of shedding are 

 well shown in Lloyd's paper, although 

 the experimental work was limited to a 

 few seasons and to eastern Upland 

 varieties. Shedding of the floral buds, 

 or "squares," is treated, as well as 

 shedding of young bolls. 



WHERE PEDICELS LET GO 



Two questions may be asked about 

 causes of shedding: why the buds'and 

 the young bolls abort, and how_they 



