324 



BACTERIAL DISEASES OF PLANTS 



Often there is a paler zone at the edge of the colony (Figs. 252 and, 

 especially, the colony in the upper left corner of Fig. 253) 

 or there may be concentric zones as in Bacterium phaseoli. Oc- 

 casionally the mottling of surface colonies on agar is so conspicu- 

 ous as to suggest an intruder (Fig. 254), but inoculations with sub- 

 cultures from such a colony produced thousands of typical spots 

 on cotton leaves (Fig. 244) and also infected the bolls typically 



FIG. 247. Rather woody cotton stems attacked by Bacterium malvacearum 

 as the result of needle prick inoculations (Nos. 103-111). Sept. 19, 1905. Photo- 

 graphed Oct. 1, 1905 but with insufficient contrast. The "black arm'' of the 

 planters. 



(Fig. 255). Moreover, after a few days, such strikingly mottled 

 colonies fill up their thin, places, as maybe seen by comparing Figs. 

 253 and 256. To these curious forms which suggest rose- win- 

 dows we have given the name "windowed" colonies. 



The colonies in + 10 peptone beef gelatin plates are also 

 characteristic. They are yellow and circular. A feeble pit of 

 liquefaction is produced and the colony sends into the depths 



