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 

 alga. 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 which include 



