1896.] MICROSCOPICAL JOURNAL. 87 



secure place in the cells for their development and in- 

 crease, but they probably make use of the products of 

 assimilation of the green plant, make use of the organic 

 substances which they, being devoid of chlorophyll, can- 

 not form. 



I have now come to the last case of the symbiosis of 

 plants with which I shall deal. It is one which is 

 of interest, both from the fact that it is the most re- 

 cently discovered case, and also because it it the only 

 case so far on record in which we have a symbiosis of two 

 small colorless organisms, both belonging to the group of 

 fungi. 



Some of you may perhaps have heard of the ginger- 

 beer plant. It is not a tree from which gingerbeer runs 

 on making an incision, nor is that popular beverage de- 

 rived from its fruits, but it is like the vinegar plant, a 

 yeast-like growth which causes fermentation. The gin- 

 gerbeer plant is said to have been introduced into Eng- 

 land by soldiers returning from the Crimean war, but of 

 that we have not sufficient evidence. This yeast-like 

 plant has the appearance of small convoluted masses, 

 and by making cultures of it a number of constituents 

 can be distinguished belonging both to the yeast-like 

 fungi and to the group of bacteria. But of all these 

 organisms two only are essential for the pure fermenta- 

 tion, a yeast (Saccharomyces pyriformis) and a bacterium 

 (B. vermiformis). This bacterium has received its name 

 from its curious twisted growth, encased in a gelatinous 

 coat, the whole resembling somewhat a wriggling worm. 

 The yeast is a small unicellular fungus growing by 

 methods of budding. (Figs. 7 and 8.) 



But these organisms are not so remarkable for their 

 shape, as for the fact that neither flourishes in the ab- 

 sence of the other. It seems probable that the fermen- 

 tative action of the yeast liberates some waste product 



