Vol. V. No. 120. 



THE AGRICULTURAL NEWS. 



375 



PARASITIC FUNGI. 



Fungi may be classed roughly into three groups 

 according to their mode of life. Some fungi obtain 

 food materials for their e.-cistenoe from dead remains of 

 plants or animals, and are known as saprophytes. 

 Others feed only upon living plants or animals and 

 cannot exist upon dead matter, and are called obligate 

 parasites, while the third and largest group contains 

 those fungi which are capable of feeding upon living 

 plants or animals, or upon dead matter. The members 

 of this last group of fungi are known as facultative 

 parasites and are undoubtedly the most difficult to deal 

 with, for they require most thorough and careful 

 treatment. 



The tungus that causes the root disease of the sugar-cane 

 belongs to the last group, and, in the West Indies, has 

 probably caused more damage, during the past few years, 

 than all other sugar-cane diseases together. (See Agricultural 

 News, Vol. Ill, p. 23.) 



Sugar planters are familiar with the appearance of this 

 ■disease in the field, where wilting and drying up of the 

 leaves are probably its first signs. The old leaf-sheaths at 

 the base of the stem, instead of being thrown off, are closely 

 matted together by a white mycelium of the fungus 

 Marasmius Saccliari. The fructifications of this fungus 

 may frequently be seen in wet weather as small, white or 

 jellowish ' toadstools ' at the bases of diseased stools, and 

 bear the spores which are capable of infecting other cane 

 plants with the disease. 



Canes that are growing vigorously and under favour- 

 able conditions are affected but little by this fungus, and 

 some varieties of seedlings appear to be more or less immune 

 from its attacks. For remedial measures, it is therefore 

 desirable to pay particular attention to the cultivation of the 

 soil in order that the canes may be increased in vigour ; it is 

 also necessary to destroy all infected material, the trash from 

 infested fields not being used in cane fields or made into pen 

 manure which is to be applied to canes. 



In the Agricultural News, Vol. IV, p. 324, it is 

 mentioned that in Trinidad a disease of bananas caused by 

 Marasmius semiustus (a fungus closely related to that causing 

 the root disease of sugar-cane) is prevalent on plants that 

 are grown in unsuitable or impoverished soils. Diseased 

 banana stems should not be allowed to remain and rot on 

 the ground, but should be destroyed by being buried deeply 

 with lime. Care should also be given to the choice of soils 

 and to cultivation, etc. 



Reference is made in the Trinidad Bulletin of Miscel- 

 laneous Information, for October 1906 (p. 133), to another 

 species of Marasmius, viz., M. graminiuin, that has been 

 found to be parasitic on the roots of grass from the lawns of 

 Government House Gardens, Trinidad, and Mr. Hart suggests 

 that this fungus may be equally responsible with the mole 

 cricket for the disappearance of grass on lawns in Trinidad. 

 This species is allied to Jfarasmitis oreades, which often 

 forms fairy rings on lawns in England. The latter is 

 eradicated by forking, and applying a 5-per-cent. solution of 

 sulphate of iron in water to the soil in the affected area. 



The ' horse-hair blight ' of tea in India and Ceylon is 

 caused by Marasmius sarmentos-us, and a very similar disease 

 occurs amongst cacao in some of the West India Islands. 

 The remedial measures suggested in each case are similar, 

 viz., that all attacked trees should be pruned, and all the 

 diseased prunings collected and burned. 



It would appear, therefore, that the genus Marasmius con 

 tains many parasitic species which closely concern West Indian 



planters, and more attention should be given to the small, 

 insignificant ' toadstools ' that are frequently noticed on the 

 different plantations, and, until they have been shown to belong 

 to fungi that are entirely saprophytic, they should be carefully 

 destroyed, together with the plant remains to which they are 

 attached. 



POLLINATION OF COTTON. 



Fear has been expressed from time to time that 

 the best varieties of Sea Island cotton being grown 

 in the West Indies might be contaminated through 

 pollen being conveyed to the flowers by wind or 

 insects from the wild cotton growing near. 



Cotton pollen is, however, so heavy and sticky, 

 that it is unlikely that it would be carried by the wind. 



In regard to the possibility of cross-pollination 

 being effected by the agency of insects, Mr. Herbert J. 

 Webber, writing in the Yearbook of the U. S. Depart- 

 ment of Agriculture (1902) on the 'Improvement of 

 Cotton by Seed Selection,' says : — 



' The cotton flower is large and attractive, and is much 

 visited by bees and other insects, so that the pollen is 

 carried from one flower to another in considerable abundance ; 

 hence in the beginning of the Department's e.xperiments 

 on cotton lireeding it was supposed that the danger of 

 cros.s-fertilization would have to be carefully avoided. 

 However, the flowers are abundantly self-fertile, setting seeds 

 normally when covered by paper bags that exclude all insects 

 and experience has shown that, while there is some crossing, 

 the large majority of seeds that set are self-fertilized. In 

 several instances, varieties have been grown in single rows 

 with other varieties all around them of such a kind that 

 crossing, where it occurred, could be easily detected in the 

 progeny. Plants grown from seed, matured under such 

 circumstances, show but few crosses, indicating that the 

 majority must have been self-fertilized. Judging from the 

 observations thus far made, it would seem that, ordinarily, 

 only from .5 to 10 per cent, of the seeds are normally 

 cross-fecundated. With cotton, therefore, it is not so 

 important to grow the plants in an isolated location as in the 

 case of corn. Nevertheles.s, practical experience has shown 

 that when growers procure a small quantity of seed of an 

 improved variety and grow this with other varieties to 

 increase their stock of seed, usually the variety gradually 

 deteriorates. This is probably due in considerable measure 

 to cross-pollination with the ordinary cotton, though, also, 

 doubtless in part to the fact that the seed received was- 

 probably highly selected, and deteriorated when selection 

 was discontinued. While the effect of cross-fertilization i.s, 

 therefore, not so great as in some plants, it is nevertheless of 

 sufficient importance to justify certain precautions being 

 taken.' 



Observations made in St. Kitt's would seem to show 

 that the honey bee is the only insect which visits the cotton 

 flower ; and further, that the way in which the bee invariably 

 enters the flower precludes all possibility of crossing, for, 

 pushing between the bracts and the corolla, the bee 

 inserts its proboscis between the bases of two petals, and so 

 entirely avoids touching the anthers or stigmas. On 

 examination of cotton flowers it will usually be found that 

 some of the anthers touch the stigmas, self-fertilization being 

 thus ensured. It would appear, therefore, that, though the 

 Sea Island cotton flower may be regarded as a source of 

 honey, it is usually self-fertilized, and there is not much 

 risk of deterioration being caused by insect pollination. 



