128 



tion of the disease due to its entrance into a new internode that 

 the odor reaches its maximum. In the softer varieties of cane the 

 odor at this stage is strong and almost penetrating. 



MICROSCOPIC TEST. 



The most decisive test of all, of course, is the microscopic 

 examination, — in fact, in some cases it is the only certain crite- 

 rion. If the spores of the fungus can be obtained, the identity 

 of the disease is at once put beyond question. 

 The sooty black appearance of the central tis- 

 sues is brought about by the formation of dark- 

 colored spores en the ends of certain mycelial 

 branches. These spores appear only after a 

 certain lenqth of time, and it is therefore desir- 



M a c- - 



rospores of the able to be able to recognize the fungus in its 

 ThfeYavio^pTil mycelial stage. This is not difficult. There 

 thTJi''l% oW'l ^I'e a number of fungi that attack cane cul- 

 S'^'Nil^^es'^* a\° t""^§"S' but of all thcsc the mycelium of the 

 tacked by Pine- pineapple funo"us alouc has certain fairlv well 



apple Disease the , ^ ^, , ^ . . 



characteristic denned characteristics. 



dark color. These .-r^. . . . 1,1 r ^ 



spores do not i he microscopic test IS conducted as lol- 



germinate at once , o 1 r .• -1 1. ^1 



but require a low^s I Search for tissue that appears to have 

 period of rest. ^^^^^ darkened bv the disease, and from such 



tissue scrape away some of the loose dark por- 

 tion with a clean tool and mount it in clean 

 water and search with a moderately high power 

 of the microscope for the characteristic spores 

 of the fungus. 



If the tissues are only recently invaded, it 

 may be that no darkening has yet taken place. 

 In that case the darkening may be quicklv in- 

 duced by giving the tissues access to air. If a 

 cane cutting in the early stages of the disease, 

 while its tissues are still only in the red stage, 

 be split open and put back together and laid in 

 a still place, such as a draw^er, in the course 

 of twelve hours its tissues will often assume 

 the dark appearance due to the formation of ^^ 



^ ^ Ihese spores 



the macrospores of the fungus. These spores e:erminate at once 



., 1 . 1 , , . . ^ , and serve to keep 



may then be examined and the diagnosis thus the disease in ac- 

 completed several days earlier than vrould other- Their^exrsSe''?s 

 wise have been possible. ^ transient one. 



Fig. 3. M i- 

 crospores of the 

 Pineapple Disease 

 Thie I a v i p s i s 

 ethaceticus. These 

 spores are smaller 

 than the macro- 

 spores and more 

 transparent. They 

 are also produced 

 in a diflPerent 

 manner, as shown 

 in Fig. 4. aris- 

 ing inside the 

 mycelium and 

 being pushed 

 forth from the 

 broken end of 

 mycelial cells. 



