336 Bulletin 167 



able that the 'off' seasons may prove to he those wherein con- 

 ditions foster this microscopic life to an unusual degree. More 

 favorahle temperature relations, or longer periods of incubation, 

 or both, in 'off' years and in the latter part of the season, might 

 reasonably be expected to promote the multiplication of organ- 

 isms in the tap-hole, spout and bucket, thus producing heavy in- 

 itial inoculation of the sap. Uncleanly methods would certainly 

 result in this condition, and in any ease, storing, even for a 

 short length of time, would serve to increase the troubles due 

 to the vital activities of microscopic organisms, particularly if the 

 temperature of the storage house was considerably above the 

 freezing point, as is apt to be the case." 



The experimental work upon which a report is submitted 

 in these pages was undertaken in an effort to determine as far 

 as might be possible the answers to the following questions: 

 What is the cause of the deterioration of maple sap? Is it 

 due to changes in composition occurring within the tissues of 

 the tree as a result of the resumption of protoplasmic activities 

 and vegetative vigor? Is it due to the action of micro-organ- 

 isms in the sap after it leaves the vascular bundles of the trunk? 

 Or is it to be attributed to a combination of these causes? 



THE RELATION OF MICRO-ORGANISMS TO SPOILED MAPLE SAP 

 The early studies, previously reported, have shown that 

 maple sap while in the vascular bundles of the tree is sterile, and 

 that when drawn without contamination and stored under aseptic 

 conditions it keeps perfectly for years, even with free access of 

 air. Hence the changes in sap known as souring are not t<> 

 be attributed to the action of enzyms present as natural in- 

 gredients or to other forms of auto-decomposition. Careful 

 studies of the microscopic flora of spoiled sap have shown that 

 micro-organisms are constantly associated with the process of 

 souring. 



In certain types of spoiled sap specific groups of organisms 

 are likely to predominate, while in other types several of the 



