129 



The structure of the fungus is such that apart from the 

 formation of the spores it may be provisionally identified from 

 the mycelium. This arises in most cases from the germina- 

 tion of the microspores or the macrospores. It is not often, in 

 all probability, that the disease is transferred from one host 

 to another "by means of the mycelium. 



The microscopic appearances of the various parts of this 

 fungus are well shown in Fig. 4. The mycelium, at 

 first colorless, becomes at last light to dark brown, though 

 never of the latter color except in the fully decomposed 

 tissues of the heart of the cane. In the partly discolored and 

 the reddish tissues associated with the onset of the disease the 

 mycelium is nearly always colorless. The mycelial cells are 

 from three to ten or more times as long as broad, and contai:i 

 refractive bodies, more particularly in the neighborhood of the 

 spore-bearing branches. It varies in thickness from three to 

 eight micromillimetres, and is extensively branched, the longer 

 branches naturally lying in the same direction as the axis of the 

 cane. 



APPEARANCE OF THE SPORES. 



The thin-walled microconidia, which germinate so easily 

 and hence serve to spread the disease rapidly, are formed in 



Fig. 4. Mycelium of the fungus causing Pineapple Disease, Tliii>lari'iji.s:s 

 ethaceticus. This mycelium is abundant in the pinkish, reddish, brownish ard 

 black tissues of cane attacked by this disease. It is a well characterized mycelium 

 and it is possible to identify it with some degree of certainty, esoecially by 

 means of the following test: If the fresh tissues containing the mycelium b'e cut 

 open and exposed over night to the air in a moist situation, the mycelium rapidly 

 produces the dark colored macrospores charactertistic of this fungus. 



The larger figures are taken from a hanging drop culture, while the figures in 

 the rectangle .in the upper right hand corner are taken from specimens found 

 among cane tissues. Two spores are shown to have germinated in the hang- 

 ing drop culture and to have begun the production of chains of microspores as 

 described in the text. Above may be seen a chain of the darker colored micro- 

 spores mentioned in the text. 



The five figures in the small rectangle may be described in order thus, be- 

 ginning at the left: First, a chain of the elliptical darker colored microspores: 

 second, a macrospore proliferating; third, regular formation of macrospores: 

 fourth, single microspore in process of formation from inside a small branch of 

 the mycelium; fifth, spore germinating and producing a single microspore. 



the cells of special nearly colorless branches of the mvcelium 

 about one hundred micromillimetres long and of varying dia- 

 meter according to the part measured, being widest consid- 

 erablv behind the middle (8 — 10 micromillimetres) and fron* 



