Cook: Malformations of Cotton Plants 



327 



duce different kinds of galls, in re- 

 sponse to the injuries of different in- 

 sects, there can be little doubt of the 

 specific effects of the insect secretions 

 in producing malformations of the 

 growing parts of plants. 



The distortions produced by the 

 mosaic diseases may be thought of as 

 relatively slight and generalized gall- 

 formations, or as analogous to the so- 

 called "witches' brooms." These analo- 

 gies would apply whether the poisonous 

 substances are supposed to come di- 

 rectly from the insects, or to come 

 from bacteria or other parasitic organ- 

 isms conveyed by the insects and able 

 to live in the cells and alter the habits 

 of growth, as in the case of the crown- 

 gall l^acteria investigated by Dr. Erwin 

 F. Smith. But instead of the definite 

 reactions seen in the formation of galls, 

 or in the abnormal branching that re- 

 sults in "witches' brooms," these mosaic 

 diseases have more generalized effects 

 through unbalancing of heredity. It is 

 conceivable that the secretions of a 

 parasite, or other poisonous substance, 

 might disturb the normal relations of 

 development in the same way that the 

 placing of plants in a new environment 

 sometimes calls forth a large amount of 

 variation. Results recently reported by 

 Mavor and Svenson of experiments with 

 fruit flies, show that exposure to X-rays 

 increased the number of cross-overs, or 

 hybrid combinations of character by re- 

 ducing the normal tendency of charac- 

 ters derived from the same parent to 

 cohere or remain associated in the hy- 

 brid progeny.* 



Varied Proportions of Diseased Plants 



Assuming that the Haitian disease is 

 of the same general nature as that of 

 China, the varied proportions of affect- 

 ed plants in the different fields in Haiti 

 is a feature of interest as throwing 

 light on the nature of the disease. 

 Such evidence was not obtainable in 

 China, because all of the plants were 

 affected. The difference may be ex- 

 plained by the great abundance of leaf- 



*Scicncc, August 17, 1023, page 124. 



hoppers in the Chinese fields, whereas 

 leaf-hoppers were not noticed in Haiti. 

 Specimens of the Chinese leaf-hoppers 

 have been identified by Mr. W. L. 

 McAtee as species of Empoasca and 

 Eupteryx. 



Many different forms and degrees of 

 distortion were observed among the in- 

 dividual plants in China, as in Haiti, 

 but in the central districts of China 

 that were visited the club-leaf disease 

 appeared universal. At least it was so 

 generally established in the fields by 

 the end of the season, that all of the 

 late growth was more or less abnormal. 

 Contrasts were afforded between the 

 normal early growth and the distorted 

 late growth, but there were no normal 

 plants to compare with those that had 

 suffered injury and distortion, so that 

 in China the idea of an external envi- 

 ronmental cause of the injuries could 

 not be so definitely excluded. 



Only one of the fields in Haiti, 

 planted to the Lone Star variety, had 

 all of the plants affected. The distor- 

 tion of the later growth in most cases 

 was great, and no individual was found 

 that was producing new normal growth. 

 The early growth had been normal for 

 a sufficient period to allow many nor- 

 mal bolls to develop, though not attain- 

 ing the full size of the variety as it 

 grows in Texas. One large plant was 

 noted that apparently had escaped in- 

 jury much longer than the others and 

 had produced larger and more numer- 

 ous bolls, but even in this plant the 

 new growth was distinctly distorted. 



Most of the fields at St. Michel were 

 of the Meade cotton, in some places 

 with the disease nearly as bad as ivi 

 the Lone Star field, in other places with 

 normal and abnormal plants mixed in 

 varied proportions. Some of the fields 

 were affected to only a slight extent, 

 with the distorted plants appearing as 

 scattered individuals, estimated at five 

 per cent or less of the plant population. 

 Only a few rods away the proportion 

 of injured plants might be much high- 

 er, showing that the agents of infesta- 



