. The actinomycetes. Actinomycetales. NAHIATIONS. MITATIOXS, AND ADAPTATION'S 99. Figure 4S. \';ui;il>ility of aclinoinyccic coioiiics in a jjhite culture i Hc^produccci from: Stanier, R. Y. J. Bacteriol. U: 557. 1942). amenable to the environment; (b) continu- ous or fluctuating variations; and (c) devel- opmental variations, resulting in saltations or mutations. The adaptive type is usually characterized by a decrease in the size of the colony, loss of the capacity to form aerial hyphae, reduction in ability to utilize certain nutrients, change in pigment forma- tion, and loss or gain in
. The actinomycetes. Actinomycetales. NAHIATIONS. MITATIOXS, AND ADAPTATION'S 99. Figure 4S. \';ui;il>ility of aclinoinyccic coioiiics in a jjhite culture i Hc^produccci from: Stanier, R. Y. J. Bacteriol. U: 557. 1942). amenable to the environment; (b) continu- ous or fluctuating variations; and (c) devel- opmental variations, resulting in saltations or mutations. The adaptive type is usually characterized by a decrease in the size of the colony, loss of the capacity to form aerial hyphae, reduction in ability to utilize certain nutrients, change in pigment forma- tion, and loss or gain in capacity to produce specific antibiotic .substances. The continu- ous type of variation is marked by the nature and intensity of the pigment formed by the organism, as well as by the capacity to pro- duce a given antibiotic. The developmental variations are also illustrated by the pres- ence or absence of aerial mycelium, pigmen- tation, and production of antibiotics. Some of these changes can be reversed to the orig- inal by growing the on special media, such as glycerol mitrient agar or sterile soil. Other \'ariatioiis or nuitatioiis are more nearly permanent or more stable in nature, although they may appear only on rare occa- sions. Examples of permanent variations are loss of , of pigmentation, and of the ability to form spores. The actinomycetes are markedly sensitive to their environment: the extent of mycelium formation can be influenced by a change in the composition of the medium. One of Lieske's cultures produced a well-developed, extensi\-ely branched mycelium in potato extract; it grew in the form of short, coccus- like chains on nutrient agar; and gave to short, sometimes branched, rods in meat extract-peptone bouillon. Waksman found that in the of S. reticuli, the sporog- enous hyphae formed verticils on synthetic agar, but showed racemose branching on nutrient agar or on certain inorganic media. Several forms of hereditary var
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