290 



THE AGRICULTUEAL NEWS. 



Septembek 18, 1909 . 



this division of plants, and will go far to explain why it 

 is that the members of it are able to attack jilants in 

 such diverse ways. Little need be said in regard to 

 bacteria, save that they are very similar to fungi, in 

 that most of them require the more complex organic 

 compounds as food; they are readily reproduced 

 vegetatively — are, in fact, rarel}- reproduced by any other 

 means: and they have the power of forming resistant 

 spores to enable the different species to survive during 

 n period of unfavourable conditions. 



In the West Indies, the commonest blights of 

 cotton are those which attack the leaves and those 

 which damage the bolls. Up to the present, the 

 species which may affect adversely the roots and stems 

 have not shown themselves to any great extent. This 

 is not the case in many other parts of the world, where 

 great losses have been experienced through the 

 ravages of such [)arasites. Considering first the leaf- 

 parasites, there are four which most commonly do 

 damage in these islands : rust, mildew, round spot, and 

 angular spot : of these, the first three are due to fungi 

 und the fourth is bacterial in origin. None of them 

 have done any extensive damage, so far : as a matter 

 of fact, the first and second are generally only found on 

 old leaves which have nearly completed their functions. 

 Nevertheless, it is easy to understand that a careful 

 watch is required in order to prevent them from 

 increasing beyond control (as they have actually done 

 in some cotton-growing countries^ that means for 

 their increase must not be pro\ided by jiermitting old 

 •cotton plants to remain in the ground, and that, e\en 

 if their presence on a plant does not result in much 

 damage to it, the fact that they are interfering to 

 a certain extent with its nutritive functions can only 

 handicap it in any struggle which it may be making 

 against other pests or untow.ird conditions. 



The blights whic-h damage the bolls are known as 

 pink spot, or anthracnose, and bla(;k boll, or boll rot; 

 each is due to a ditlerent fungus. In the first case the 

 lint is only attacked if the boll is young ; in the second 

 its contents are completely destroyed and it fails to 

 open. In anthracnose the attack begins from the out- 

 side, and the sunken black spots with pink edges are 

 an unmistakable sign of the presence of the disease. 

 In black boll, the disease starts inside the boll, often 

 near the base, and its contents are gradually changed 

 into a (lark-coloured, slimy mass of swollen, partially' 

 germinated seeds, or the boll ma}- dry up on the plant 

 and open slightly. Notwithstanding this far-reaching 

 internal change, the exterior of the boll is of a healthy 

 •colour, the only external signs of the presence of the 



disease being that the boll becomes spherical, instead 

 of oval, and tapers quickly to a sharp point, while it is 

 more resistant to pressure than a healthy one. Black 

 boll only affects the fruits, while anthracnose may be 

 communicated from old plants to young ones, attacking 

 the cotyledons ami stems of these, and to other old ones 

 w^here it is found on the dying leaves and injured parts 

 of the stem. Preventive measures are the best for 

 these diseases. They include: the destruction of old 

 cotton, the selection of seed from healthy plants, and 

 the disinfection of this seed before planting. 



The shedding of bolls has not been shown to be due 

 to the attack of any blight or blights. It is caused by 

 a physiological condition of the plant, in which an effort 

 is made to throw otf bolls which have no chance of 

 becoming mature, in order that the remainder may be 

 given the best opportunity of doing so. This state 

 may arise from injury to the plant, such as root-cutting 

 by deep cultivation : unfavourable environment, as for 

 instance, a caked or weedy soil, exposure, overcrowding, 

 or an excessive stimulus toward vegetative growth : and 

 sudden climatic changes, due either to ilrought or 

 excessive rainfall. Good drainage and improved cultiva- 

 tion are the only remedies for this. 



The careful cotton planter will keep a constant 

 watch for the appearance and spread of these fungous 

 and bacterial diseases, so that, in the event of their 

 assuming serious proportions, he will he ready to 

 combat them. At the end of the crop he will recognize 

 the importance of the destruction of the plants which 

 are no longer a source of profit but rather of danger 

 to him, as well as^to others. Finally, in any scheme of 

 selection of seeds, he will see that these are chosen from 

 plants that are healthy and disease-resisting, in order 

 that this property may be handed on in the strain of 

 cotton that he is trying to evolve. 



Reference is made, in conclusion, to the publica- 

 tions of the Department that should be consulted in 

 this connexion, namely : the ^1 B C of Cotton Planting, 

 (Pamphlet No. 45), the West JixIiiDi BuUctni, 

 Vol. IV, p. 2.5.5: Vol. V, p. ITS: Vol. VI, p. 117: 

 Vol. IX, p. 210, and to articles on the subject that 

 have appeared from time to time in the A(/ricidtund 

 News. Observations on the plants in the field should 

 be accompanied by a perusal of these: in this way, the 

 ability speedily to discover and identify any of the 

 diseases will be gained. Not only this, but, in the 

 event of a serious sj)read of them the cultivator will be 

 already in possession of a knowledge which will enable 

 him to (K'al with it, and no time will be lost in search- 

 ing for remedies. 



