380 Bulletin 167 



one suspects physiological changes occurring- within the tree. 

 These results do not agree with those obtained in 1909, and cited 

 in bulletin 151, as well as on pages 357-358 in this issue; but 

 the contradiction may probably be explained by the divergen- 

 cies in the prevailing weather conditions during the two sea- 

 sons. The spring of 1910 was interrupted by periods of warm 

 weather which started the trees into vegetative activity at 

 least two or three weeks before the close of the sugar season, 

 whereas the season of 1909 was short and exhibited no warm 

 periods intervening with cold spells. 



The small amount of invert sugar present in No. 87 con- 

 firms the suggestion obtained from the results of 1909, that the 

 invert sugar content of a sap tends to decrease rather than in- 

 crease as the season advances. 



Inoculation Experiments in 191 i 



The considerable number of instances in which the plates 

 from incubated samples failed to return approximately pure cul- 

 tures of the introduced organism in 1910, led to a modification 

 of the procedure for 1911. The incubation buckets were dis- 

 carded and a large number of 2 quart glass preserving jars were 

 secured in which the sap was placed and subjected to fractional 

 sterilization before inoculation. The covers were left on the 

 jars but were not clamped down, so that the protection from in- 

 fection was approximately the same as is afforded in Petri dish 

 cultures. For purposes of sterilization, the jars were placed in 

 a steam chamber and treated as is customary in sterilization with 

 flowing steam at atmospheric pressure. Except in the last series 

 of the season tbe sap was subjected to two sterilizations only. 

 The last series was steamed on each of three consecutive days. 

 This change was made because one of the jars of the control of 

 the preceding series developed cloudiness, which was found upon 

 examination to be due to spore-bearing organisms of the subtilis 

 type. As in the preceding season, the success of the inoculation 

 experiments was controlled by bacteriological examination in 



