130 



thence tapering to the open end from which the micro- 

 spores are escaping. These are cyhndrical, nearly colorless, 

 measure about five micromillimetres in diameter by ten to four- 

 teen micromillimetres long, and occur in or outside the cells of the 

 mother mycelium in numbers up to twenty, but generall}' less than 

 half this number. These spores are sometimes seen to be of smaller 

 size, ellipsoidal form, with a thicker wall and darker color. These 

 dwarf spores are, however, produced row-wise inside the cells 

 of the mycelium, and all possible intermediate stages connect 

 theni with the regular microspores. 



The dark-colored macrospores, which in the later stages of 

 the attack impart to the diseased tissues their dark color, are 

 borne in an entirely different manner and have an entirely dif- 

 ferent function. They are far larger than the microspores, 

 measuring lo — 12X1*^^ — 19 micromillimetres, and are more or 

 less ellipsoidal in form. The brownish to blackish wall is thick 

 and impervious. The ends often indicate the position of the 

 previous attachments, so that the contour is not exactly ovate 

 or ellipsoidak Though these conidia are usually borne in 

 chains at the ends of special branches it is not infrequent to 

 find them borne singly. This is usually brought about, I think. 

 liy the falling away of all the members of the chain except the 

 proximal one. 



The microconidia germinate promptly and easily, merely in 

 the presence of moisture. The macrospores germinate with 

 much greater difficulty, and only after a period of rest. 



From this quotation the reader may acquire a very fair idea 

 of the fungus as it occurs in cane. The characteristic pipe 

 mentioned in connection with the stalk of the cane plant is 

 never seen, of course, in the pineapple. Moreover, the rot 

 presents certain peculiarities in the pineapple that call for spe- 

 cial mention. These points will now be taken up and dis- 

 cussed in order. 



THIELAVIOPSrS IN PINEAPPLE. 



Taking sections of one of the carpels at a point a few milli- 

 meters from the surface of a pineapple that has only just be- 

 gun to show traces of the sooty blackness due to the formation 

 of the black macrospores, and at a distance of two to four 

 inches from the dark macrospore formation, one may see that 

 the already watery tissue is mainh^ composed of the mycelium 

 of the Thidaviopsis. The mycelium is easil}^ distinguished, as 

 it is darker in color than the other tissues and than most 

 mycelium. In this colorless part one mav see that the for- 

 mation of the microspores precedes that of the macrospores. 



