162 



PHYSIOLOGICAL BOTANY. 



Some Bacteria separate into spores ; and diseases in men as well as plants 

 are believed to be due to the presence of Bacteria. They are parasitical or 

 saprophytic, feeding on living or decaying matter; they are the agents of de- 

 cay and revel upon the ruins they produce. As they multiply by fission, they 

 are called Schizomycetes (^x^, to divide, and M^S, a fungus). (Fig. 512.) 



\ \ 





512 



512, A, Bacterium Termo, magnified to 1,000 diameters, undergoing the process of fission. JB, Same, 

 magnified to 3,COO diameters, in which the process of fission is nearly completed. <7, Micrococci (x 1,000) 

 undergoing fission, the new cells arranging themselves in curved and crooked lines or in irregular groups. 

 D, Sarcina Ventriculi (x 1,000) undergoing fission in two directions, the new cells arranging themselves in 

 square groups. 



411. The Yeast Plant (Fig. 513) is one of the most 

 interesting of the unicellular organisms ; it is the agent 

 of fermentation, and plays an important 



part in bread-making, where it disinte- 

 grates the starch-grains in the flour, and 

 thereby liberates carbon dioxide ; the gas ^ , 

 set free struggles to find its way through 513 



513. Yeast Plant, Sac 



the dough, becomes entangled, forms cav- charomyces cerevisi*. 

 ities in the mass, and makes it sponge-like or light. 



412. The next grade above the plant which is a 

 single cell is one composed of a mass of cells without 

 a special axis of growth ; as some of the Sea-weeds, 

 which are mere masses of flat cells arranged in two 

 layers, forming irregular leaf-like expansions. 



