[haerison a barlow] nodule ORGANISM OF THE LEGUMINOSAE 17S 



ing 146 days, each containing 250 grams of medium, was ^ gram per 

 day, at which rate the medium would be exhausted in 1,000 days. 

 These flasks were simply plugged with cotton and the cultures were 

 g^o^\'n in a living room heated by steam. The loss was less from a 

 series having parclrment paper tied over the mouths of the flasks. In 

 this case, the medium would have been exhausted in a little less than 

 three years. The plants grew vigorously in the agar, especially at first; 

 later, uninoculated plants gradually withered or even died as if from 

 nitrogen starvation. The inoculated plants easily thrived as long as 

 they were kept. 



Contaminating bacteria and moulds sometimes appeared in the 

 flasks a few days after the seeds were planted in them; these were 

 without effect on the plant and were never obser\'ed to cause or inter- 

 fere with nodule formation. 



In all inoculated flasks nodules appeared usually in about a month. 

 They were sometimes few and large, sometimes many and small; in 

 one case as many as 70 developed on the roots of one plant. The 

 nodules continued to increase measurably in size as long as the cultures 

 were observed and were about the same form as seen on plants in the 

 field, but occasionally larger. In the absence of root hairs, infection 

 began as a small transparent spot in the root. Nodule formation and 

 general infection of the root appeared to check extensive root form- 

 ation. In all inoculated flasks growth of Ps. radicicola was copious 

 and characteristic, spreading as a thin layer over the agar and pene- 

 trating the agar along the roots so that each root was surrounded even 

 to its growing tip with a cylinder of growth. 



On final examination, Ps. radicicola was found by stains and by 

 plate cultures in the medium of the inoculated flasks and no other 

 organisms were present, or in some cases moulds and other bacteria 

 were found. 



A general infection of the roots generally accompanied nodule 

 formation. 



The stains from the nodules showed that simple rods sometimes 

 prevail and sometimes branched and irregular forms. 



I^odules were never formed and root infection was never obser\'ed 

 in uninoculated controls. 



The presence of Ps. radicicola was never detected by staining nor 

 by cultures in uninoculated controls, where bacteria and fungi were 

 absent or sometimes present in the medium, but never in the living 

 roots. 



The species on which nodules have formed in flask cultures on ash- 

 maltose-agar are PJiaseolus vulgaris. Vicia villosa, Pisum sativum and 

 Glycine hispida. 



