Bacterial Disease of the Squash-bug. 345 



In four days the dish from the original tube gave 

 abundant colony formation, and in the next dish about 

 ten colonies appeared. The surface colonies were circu- 

 lar, slightly yellowish white or dirty white, but with a 

 distinct opalescence. The submerged colonies were ellip- 

 tical or slightly pyriform in vertical projection, growing, 

 toward the surface, more and more laterally compressed. 

 This peculiar growth of submerged facultative anaerobic 

 bacteria has been well explained by Professor H. Mar- 

 shall Ward,* who has studied in detail under high pow- 

 ers the formation of micro-colonies in certain cell cul- 

 tures. The horizontal long diameter of such elliptical 

 colonies is in the plane of fission of the rodlets. The 

 form of growth is due to the fact that as the elongating 

 rods are broken up into daughter cells, these cells slip 

 by each other (one over the other) under the pressure 

 of the contracting gelatine or agar; and if in agar, evi- 

 dently this form will be retained in the macro-colony. 

 To return to the circular colonies, those that had room 

 for the fullest development showed in a few days marlced 

 lobulations, and sometimes beautiful fan-like radiations. 

 Furthermore, those submerged colonies that had reached 

 the surface took on the circular form and very soon de- 

 veloped some of the characteristic radiations, although 

 the growth is thinner than when they develop superficially. 

 All stages of these developments are evident in Plate 

 XXVIII., Fig. 1. Submerged colonies appear deeper 

 colored than the surface ones, but this is only an ap- 

 parent coloration. It will also be seen that there is a 

 film-like growth on the lower surface of the agar be- 

 neath deeply submerged colonies. This, also, is the same 

 form which has spread out between the contracted agar 

 surface and the glass. 



The lobulated growth appearance is not always pres- 

 ent, even in cultures direct from the insect, and like all 

 such radiating bacterial growths, is probably greatly 



* "Thfi Formation of Bacterial Colonies" (Annals of Botany, Vol. IX., No. 

 XXXVI.. Dec, 1895.) 



