FIELD STUDIES OF THE DISEASE. 49 



for at least the last three years, but is only at present beginning to 

 be serious on the leeward side. 



Considering the examples as a whole, it seems difficult to find a 

 definite case of the spread of the infection in any one direction. The 

 most favorable example for this theory is that of the condition of the 

 groves in the Macanagigua Valley and toward El Yunque — that is, to 

 the south, nearly in the direction of the prevailing \vind. The disease 

 spread from the valley to the hilltop inland and then crossed the hill- 

 top and has since gone a few miles farther south into the valleys. 

 Even this is not a clear-cut exaihple, as a closer study of it reveals. 

 As already stated, a careful study was made of one grove in this region 

 during the year 1908-9. Figure 10 shows the condition of the grove 

 on March 10, May 28, August 5, and October 21, 1908. The lower 

 right-hand side of each section of the diagram represents the wind- 

 ward side of the grove. Section a shows, however, that there are 

 more healthy trees standing on that side than on the leeward side, 

 represented on the diagram by the upper left-hand corner. The 

 straight horizontal dash indicates diseased trees that have been cut 

 down or destroyed. In sections c and d it will be seen that the lee- 

 ward side is almost destitute of standing trees, either diseased or 

 healthy. It mil further be found that there are many trees repre- 

 sented in the lower left-hand corner that have become diseased and 

 that are somewhat to the windward of the first lot. Perhaps the 

 most striking thing shown by the diagram is the sporadic nature of 

 the spread of the infection. It seems difficult to attribute this to 

 wind. 



An entirel)^ different argument and one opposed to the idea of 

 wind as the distributor of the germ is the nature of the infection. 

 The diseased tissues consist of a soft, wet rot in the heart of the 

 crown and surrounded by the hard tissues of the leaf bases and 

 sheaths. It is difficult to conceive of the wind getting at such a 

 location and blowing about moist bits of tissue. It is true that 

 many forms of bacteria are carried about in the air, but they are forms 

 that are able to withstand considerable desiccation and are usually, 

 if not always, sporulating forms. The organism causing bud-rot is 

 not, so far as known, a spore former and can not mthstand sufficient 

 drying to permit of its being blown about like so much dust. 



In contrast to the idea of %vind as a disseminator of the germs is 

 the belief of many that insects, or birds, or some form of animal life 

 is responsible for this trouble. If this were the case, the spread of 

 the infection would occur in just such a sporadic manner as shown 

 in figure 10, sections a to d. As seen in the field the evidence all 

 tends to point in this direction. If the insects that may carry the 

 disease are flying forms, it would explain the occasional apparent 

 6389°— Bui. 228—12 4 



