258 GENERAL BOTANY 



secretions giving rise to disease. The ptomaines are regarded by 

 some as bacterial secretions and by others as by-products of the 

 decomposition caused in organic material by various saprophytic 

 bacteria. Ptomaine poisoning is more likely to occur in warm 

 weather, since conditions are then more favorable to general 

 bacterial activity. 



SUMMAEY 



From the above discussion it has been found not only that bac- 

 teria have the same general cell structure as other organisms but 

 that their physiological activities and products closely resemble 

 those of the yeasts and other saprophytic and parasitic fungi to 

 which they are most closely related. The decay and putrefaction 

 caused by bacteria is indirectly a result of certain digestive and fer- 

 mentative processes which belong in the same category as similar 

 nutritive processes occurring in yeasts and other fungi. Even the 

 disease-producing power of bacteria is due to products of their cell 

 protoplasts, which are not peculiar to the bacterial cells alone. The 

 striking effects of bacteria on other organisms and upon organic 

 material are due, therefore, to their great numbers and to the im- 

 mense scale upon which they act, rather than to any marked pecu- 

 liarity either in their organization or in their physiological processes. 



MOLDS 



Everyone is familiar with the appearance of molds on bread, 

 jelly, and other household products. The white, fluffy character 

 of the molds is due to the innumerable colorless filaments 

 which comprise the plant body. These filaments are individually 

 called hyphce, while the entire white mass of filaments consti- 

 tuting a mold colony is called a mycelium. The hyphse of the 

 molds, and other fungi as well, resemble very closely the fila- 

 ments of green algse like Vaucheria or Spirogyra, except that 

 they lack chloroplastids and green chlorophyll. The mycelium 

 which is formed by them usually occurs both on the surface and 

 within the substances upon which they grow. The term aerial 

 hyphce or aerial mycelium is applied to the visible surface filaments 

 of a mold, while those which grow within a substance are called 

 submerged hyphce or submerged mycelium (Figs. 139 and 140). 



