CAUSES OTHER THAN BACILLUS COLI. 147 



For this reason many of the theories as to the cause of the disease 

 may have a grain of truth in them in that the causes assigned may 

 be auxiliary, though not primary, factors in producing the diseased 

 condition. Such being the case, it is desirable to discuss briefly 

 these factors and the probable rehitive amount of their influence. 



In soils containing too much lime, lack of good drainage is proba- 

 bly the imraecUate cause of the trouble. Trees growing in such soils 

 are rather slender, and have yellowish leaves, and either fail to bear 

 fruit or produce an imperfect fruit. In addition to poor drainage 

 an excess of lime in an insoluble form may have some direct effect 

 upon the roots which will produce in the crown an appearance sim- 

 ilar to drought. 



Soils consisting too largely of clay are heavy, cold, and damp. 

 Under such conditions stagnation follows, the roots are not able to 

 absorb water with sufficient facility, and injury results. 



The question of the amount of salt (NaCl) desirable in the soil has 

 been much debated. It is claimed by some investigators that a very 

 small proportion is necessary, no more than may be found in an 

 average soil whether near the sea or remote from it. Others main- 

 tain that placing about the roots of the tree a small quantity of salt 

 and mixing it with the soil benefits the tree greatly. Wliether a 

 reduced cjuantity of salt would so aft'ect the tree as to render it easy 

 to succumb to the bud-rot is not easy to determine. There has been 

 no work done as yet to ascertain tliis. 



In the case of soils either constantly or temporarily too dry there 

 is certainly a weakening of the vitahty of the tree. It is difficult to 

 distinguish this condition from the one in which there is an excess 

 of water. It would seem probable that the latter condition would 

 be the most suitable for bacterial growth. Comparison of the spread 

 of the bud-rot in rainy weather with that in dry weather incHnes the 

 writer to say that the rainy weather is more favorable, although the 

 difference is not very strildng. The eft'ect may depend not so much 

 upon a large amount of moisture as on an upsetting of the balance 

 of chemical constituents of the tissues by any such untoward con- 

 ditions as drought or excess of moisture. 



In the matter of insects occasioning the trouble in the coconut 

 trees Dr. Carlos de la Torre (p. 22) has maintained that the scale 

 insects covering the stomata of the leaves tend to suffocate the 

 plants, i. e., prevent transpiration, and in that way render the tree 

 susceptible to the disease. It can scarcely be denied that a hin- 

 drance to the proper amount of transpiration would seriously affect 

 the health of the trees and possibly in that way furnish an oppor- 

 tunity for the work of the bacteria. From the examination of 

 numerous trees affected with bud-rot, where the scale insects were 



228 



