64 The Botanical Gazette. ' l March ' 



is the predominating fungus in the last stages of the disease 

 giving a black appearance to the entire leaf. 



Much speculation in agricultural papers has been indulged 

 in regarding the cause of ' 'black rust" of cotton. It is not 

 proposed in this preliminary note to critically examine the 

 various theories propounded. Some of my correspondents 

 who formerly attributed the disease to the peculiar condition 

 of the soil, lack of fertilizers, etc., say that sometimes in the 

 best soil and with careful fertilizing the disease appears in a 

 very destructive form. That has been abundantly proven 

 during the past year under my own observation. Cercospora, 

 Colietotrichium and Phyliosticta are all active parasites, and 

 I am convinced from a year's study that Cercospora Gossypina 

 is a more active and destructive parasite than has been form- 

 erly regarded. A diseased condition once started by such a 

 fungus opens the way for the rapid growth and great injury 

 produced by such forms as Macrosporium and Alternaria. It 

 is possible the Macrosporium may infect the leaves unaided 

 by other fungi. Inoculations of plants free from other forms 

 must be made to determine this. 



Cercospora Gossypina sometimes produces a serious spot 

 disease of the cotyledons. I first observed this on some 

 young plants started on the horticultural grounds, in Septem- 

 ber, for experimental purposes. I am told that sometimes in 

 cold seasons in May this spot disease is quite injurious along 

 with "sore shin." 



While in North and South Carolina my attention was called 

 to a disease termed "red rust" which was chiefly characterized 

 by a reddening of the leaves not produced nor accompan- 

 ied by any fungous growth. In most cases this seems to 

 be due to some condition of the soil which induces a hastened 

 maturity of the plant and the development of erythrophyll in 

 the cell sap of the leaves. In some cases the development of 

 erythrophyll is induced by the irritation of mites as I have 

 proved by infection experiments. From several places in both 

 states cotton quite severely injured by mites has been sent me. 

 An account of this was published in Bulletin no. 4 of the South 

 Carolina Agricultural Experiment Station, January, 1889. 



The reddening of the leaves by the development of ery- 

 throphyll in the cell sap of the leaves is very common in some 

 soils in Alabama and probably in all the cotton-producing 

 states. It is quite possible that all through this belt there 



