190 



ROBERT A. BUDINGTON. 



would be of more importance in case the solutions were employed 

 for prolonged periods; but in this work the bacterial factor 

 never seemed to interfere with entirely healthy root growth. 

 Indeed, Curtis has shown that, in some instances at least, a 

 heavy infection of bacteria and fungus filaments about root 

 sprouts on cuttings seems to be favorable to their better growth. 

 His experiments covered many weeks, often months; deleterious 

 effects due to carbon dioxide production in the solution may 

 follow such infection after extended periods; but the factor is 

 negligible in experiments limited to ten-day or two-week periods. 

 The following photograph is essentially self-explanatory and 

 may be taken as typical of many. Roots grew somewhat in 



0.75 



FIG. i. Onion bulbs growing in Pfeffer's nutrient solution, in which is dis- 

 solved desiccated thyroid gland material, in parts of a grain indicated. 



solutions of each different strength here mentioned; the very 

 slight growth in the left hand bulb here figured would have con- 

 tinued to greater length after a time, but the proportionate 

 lengths w r ould have remained much as when the picture was 

 taken. The apparent influence of the thyroid material is to 

 retard growth rate. 



