298 INTRODUCTION TO THE STUDY OF FUNGI 



attributed to the presence of bacteria. In 1891 Dr. Halsted 1 

 apparently determined that a rotting disease of cucumbers 

 and melons was caused by microbes, and that not only could 

 healthy plants be infected, but the virus could be transferred 

 to tomato plants, rapidly producing decay. The destructive 

 " Peach yellows," which long baffled all efforts to discover its 

 cause, has been found to contain these organisms, and efforts 

 are being made to trace its bacteriological relationships. 

 Finally, the pear blight which Dr. Burrill investigated in 

 1880, and which is sometimes called "fire blight," was finally 

 determined in 1884 to be the result of the attacks of Micrococcus 

 amylovorus, otherwise named Bacillus amylovorus. In this 

 species, although the formation of zooglaea has never been 

 observed in the tissues of the tree, or upon solid media, they 

 occur with much regularity in fluid cultures, when placed 

 under favourable conditions for rapid growth. They are 

 produced to some extent throughout the fluid, but are most 

 abundant in the thin pellicle which forms upon the surface. 

 They often appear the more distinctly by being surrounded by 

 a colourless layer, free of bacteria, which is an extension of 

 the basal stratum of the zooglaea mass. This branch of the 

 inquiry is, however, of such recent origin, and is in such 

 elementary condition, that it would be imprudent to affirm too 

 much, or indulge too freely in speculation. 



Thus much, then, for the Microbes, which are regarded 

 generally, and spoken of, as the organisms which are instru- 

 mental in producing putrefaction. It is remarkable what a 

 voluminous literature has already accumulated, within a few 

 years, which may be accepted as some evidence of its im- 

 portance. The subject may not affect business interests so 

 much as the cognate one of the Fungi of fermentation, but it 

 is more than suspected that it has a very intimate relation to 

 life and death. 



The yeast Fungi are very simple and low forms of vegetable 

 life, although of a more imposing size than the Schizomycetes, 

 or Microbes, to which we have given brief attention. The 

 yeast Fungi, which are the agents of fermentation, are repre- 

 sented in old books under the name of Torula cerevisiae, and 



1 Gardener's Chronicle, 3rd June 1893. 



