164 BACTERIA IN RELATION TO PLANT DISEASES. 



Thiothece \Vinogradsky. 



Families inclosed in a thick gelatinous cyst. Cells capable of swarming and 

 very loosely embedded in a common gelatin. When the swarm stage supervenes, the 

 cells lie more loosely, the gelatin is swollen, and the cells swarm out singly and 

 rather irregularly. 

 Thiodictyon Winogradsky. 



Families consisting of rod-shaped cells having their ends united into a net. Out 

 of an originally compact mass of rods there gradually results from rearrangement a 

 Hydrodictyon-like cell-union, which, under unfavorable conditions, may again draw 

 together into a compact mass of rods. The multiplication of the families results from 

 division or by loosening of slowly motile small cell-colonies. 

 Thiopolycoecus Winogradsky. 



Families solid, non-motile, consisting of small cells closely pressed together. 

 Multiplication of the colonies by the breaking up of the surface into numerous short 

 shreds and lobes which continue to split up into smaller heaps. 



(V) Subfamily CHROMATIACEAE. 



Cells free, capable of swarming at any time. 

 Chromatium Perty. 



Cells moderately thick, cylindric-elliptical or elliptical. Polar flagella. 

 Rhabdochromatium Winogradsky. 



Cells rod-shaped or spindle-form, with flagella on the poles. 

 Thiospirillum. 



Cells spirally twisted. 



To the preceding may be added a third order, Myxobacteriacese, which is not 

 discussed critically by Migula and is not adequately described in any of the text- 

 books. The following general characters are taken from the papers of Dr. Roland 

 Thaxter, to whom we owe our knowledge of these curious and interesting organ- 

 isms. The most recent paper is by Erwin Baur, Myxobakterieii-Studien, Archiv fur 

 Protisteukunde, V Bd., I Heft, pp. 92-121, i pi. 



MYXOBACTERIACEAE. 



Motile, rod-like organisms, multiplying by fission, secreting a gelatinous base, 

 and forming pseudoplasmodium-like aggregations before passing into a more or less 

 highly developed cyst-producing, resting state, in which the rods may become encysted 

 in groups without modification, or may be converted into spore-masses. The vegeta- 

 tive rods, which vary little in size and form in the different genera and species, are 

 typically elongate, sometimes reaching 15 /< in length. Cell-division follows an 

 elongation and nearly medium constriction of the rods, which, except at the moment 

 of division, are always separate; never united in chains. A slow, sliding locomotion 

 and a Beggiatoa-like, bending motion is characteristic of the active rods. Organs 

 of motion have not been detected. In all species, with one exception, the rods, 

 when seen in masses, are more or less distinctly reddish. A distinct, firm, hyaline, 

 gelatinous base is secreted by the colony as it extends itself, over which the individuals 

 may move or in which they become embedded. 



The vegetative period, in artificial cultures, usually lasts about a week, or even 

 two weeks, but in nature the production of cysts must be more rapid. Common in 

 moist situations on dung, decaying wood, fungi, lichens, etc. According to Bauer 

 they grow best at 30 C. 



