208 THE STORY OF THE PLANTS. 



due to their habits only. In short, we call any 

 cellular plant a fungus, if instead of supporting 

 itself by green cells, it has adopted the trick of 

 living on organised material already laid up by 

 other plants or animals. 



Among these fungus-like plants, again, some 

 of the simplest and lowest are the celebrated bac- 

 teria, which are one-celled organisms, living in 

 stagnant or putrid fluids, and also in the bodies 

 and blood of diseased animals. They answer 

 among fungi to the one-celled alga. Many of 

 them cause infectious diseases ; such are the bacilli 

 of diphtheria, typhus, cholera, consumption, small- 

 pox, and influenza. Surrounded by a suitable nu- 

 tritious fluid, these tiny parasitic plants increase 

 with extraordinary and fatal rapidity. Though 

 they are really one-celled, and reproduce by cell- 

 division, they often hang together in rude lumps 

 or clusters which simulate to some extent the 

 many-celled bodies. In this book, however, where 

 we have concentrated our attention mainly on the 

 true or green plants, I have not thought it well 

 to dwell at any length on the habits or structure 

 of these animal-like organisms. 



Another well-known group of small fungus- 

 like plants is that which contains the yeast-fungus, 

 a one-celled plant, which reproduces by budding. 



The higher fungi are many-celled, and often 

 possess well-marked organs for different purposes. 

 They answer rather to the seaweeds and higher 

 algce. Familiar examples are the common moulds, 

 which form on jam, dead fruit, and other decay- 

 ing material. Some of them, like the smut of 

 wheat and oats, are parasitic on growing plants, 

 and most dangerous enemies to green vegetation. 

 The highest fungi are the groups w T hich include 



