36 VEGETABLE HISTOLOGY. 



CHAPTER IV. 

 BACTERIA (SCHIZOMYCETES, OR FISSION MOULDS). 



One of the classes of the Thallophyte series of plants is the 

 Schizophyta. This class is composed chiefly of the Schizomy- 

 cetes or Bacteria. These are extremely low forms of plant life, 

 being exceedingly simple in structure and always minute, some 

 of them being the smallest of known organisms. They are 

 mostly unicellular, or, if consisting of cell-aggregates, as is 

 sometimes the case, the cells are united in a simple way and 

 have very little dependence upon each other. They are the 

 most abundant of organisms, the largest being not more than 

 Vioooo i ncn i n diameter and the smallest not more than 1 / 10 of 

 that. All are chlorophylless, i. e., without coloring matter. 

 The cells agree in having mostly rigid transparent walls and 

 colorless cell-contents, but different species differ considerably 

 in form, size, etc. Their usual mode of increase is by fission 

 or splitting, but they also produce very minute so-called spores 

 by a method known as internal cell-formation. (See later.) 



In some species the cells, after fission, immediately become 

 independent; in others they remain united for a time, to form 

 filaments or chains of various lengths. Many of the species in 

 some stage of their development have the habit of secreting a 

 jelly and increasing rapidly by fission, forming large gelatinous 

 colonies. These are called sodglwa-masses. "Mother-of-vin- 

 egar" and the so-called "blood-rain," consisting of red gelatin- 

 ous spots often found on putrefying bread, are examples of 

 zoogloea-masses. 



In all putrefying fluids or solutions that contain decaying 

 organic matter bacteria swarm in myriads. They are, in fact, 

 the inciting cause of putrefaction. By their agency also milk 

 sours, wine is converted into vinegar, etc. So far as animal life 

 is concerned, some of the species are harmless or perhaps even 

 beneficial, while others are the source of some of the most 

 dreaded and most fatal of diseases. Chicken cholera, splenic 

 fever, typhoid fever, diphtheria and leprosy are examples. A 

 peculiar interest therefore attaches to the study of these 

 organisms. 



Bacteria are killed at about 70 C. or above, but the spores 

 can, in many cases, survive a temperature above 100 C. 

 (Spores are little specialized cells which have the power of 

 developing into cells or plants in all respects like the ones from 

 which they were derived. In the case of bacteria they are 

 formed for protective and not for reproductive purposes; they 

 can withstand conditions of temperature, etc., under w^hich the 

 ordinary cells die and thus ensure the survival of the bacteria.) 



Bacteria are conveniently grouped according to their shapes. 



