Cook: Malformations of Cotton Plants 



329 



seems to be no break in the series that 

 would require the assumption that two 

 or more diseases are involved. Many 

 of the abnormal plants probably could 

 not be distinguished from extreme 

 cases of degenerate "rogues" or perju- 

 gate hybrids, and these factors of 

 diversity were present also in the mixe<l 

 fields. But the disease injuries were 

 equally severe in the more uniform un- 

 iliixed stocks, grown from newly im- 

 ported seed. 



It may not appear reasonable to sup- 

 pose that so much diversity arises di- 

 rectlv from one cause, unless it is con- 

 sidered that the diversity is in the 

 plants rather than in the disease, so 

 that the disease is considered as a dis- 

 turbing factor rather than as a defi- 

 nitely directive agency, such as the in- 

 sect secretions that produce galls. This 

 distinction makes it possible to think 

 of the disease as disturbing the growth 

 of the new tissues, without affecting 

 the tissues already formed. In some 

 of the mosaic diseases where seed has 

 been grown from affected plants the 

 seedlings proved to be normal, which 

 would indicate that the germ plasm is 

 not affected, but only the growth proc- 

 esses. 



The Disease Not Contagious but 

 Infectious 



It was plain that the disease was not 

 contagious in the ordinary sense, but 

 required some active agent of transmis- 

 sion that had been present temporarily, 

 and had later disappeared. Later in- 

 fections must have occurred, if insect 

 conveyors of the disease had continued 

 to work in the fields after some of the 

 plants became affected. Such evidences 

 of spread of infection were looked for 

 in places where the injured plants were 

 few, but the uninjured plants remained 

 normal to the top, while adjacent indi- 

 viduals had been crippled from an early 

 stage of growth, when the stalk was 

 only six to eight inches high. 



That only a few plants were injured 

 in some places may be due to small 

 numbers of insects that were present, 

 or to the sources of infection being 



scarce or remote. The occurrence of 

 such a disease, and the extent of injury 

 might vary greatly with the seasons, 

 depending upon the abundance of in- 

 sects or upon the existence of the dis- 

 ease in a native host-plant of the in- 

 sects. Hence it would seem desirable 

 to study the native cotton and related 

 plants as having possible relations to 

 the occurrence of the disease. Since 

 the period of insect activity may be 

 short, the season of planting might 

 largely determine the amount of injurv. 

 Earlier planting might secure more 

 growth in advance of the disease, while 

 plantings made late enough might 

 escape entirely. 



The only disease or disorder of cot- 

 ton thus far recognized in the United 

 States as possibly analogous to the 

 Chinese and Haitian diseases is one 

 that has attracted attention for the last 

 two or three seasons in the Salt River 

 Valley of Arizona. The popular name 

 "crazy-top" is being applied by the 

 farmers, on account of the abnormal 

 branching and sterility of the upper 

 part of the plant. The abrupt change 

 from the normal growth and branching 

 of the lower part of the plant is a fea- 

 ture of similarity with the mosaic dis- 

 eases. 



Sterility and abnormal branching 

 habits are the more notable features of 

 the disease in the Pima or Egyptian 

 type of cotton, but in the Upland varie- 

 ties that are now being planted in the 

 Salt River Valley there are more 

 pronounced symptoms of reduction, 

 crumpling and crowding of the leaves, 

 which may represent the same disorder. 

 The branching of such plants is dis- 

 tinctly abnormal, with many axillary 

 shoots, decurrent stipules, or fascia- 

 tions. The floral buds and bracts also 

 have a very restricted development, so 

 that few bolls are produced, and these 

 usually are very small. 



The occurrence of the "crazy-top" 

 injury is also very erratic, with no 

 apparent relation to cultural conditions. 

 The injured plants may be sprinkled 

 indiscriminately among normal indi- 

 viduals, or in some places a majority 



