8 BULLETIN 10^0, U. S. DEPAETMEXT OF AGPJCULTUEE. 



tained from the last two. All of these were conducted at chronic 

 nonhatch points. 



Those clusters placed in the wire cages were entirely removed from 

 any influence the trees might have upon them and were fully ex- 

 posed to all actions of the elements. Very little information was 

 obtained from this series beyond the fact that clusters reacted the 

 same waj' no matter how they were placed. 



During the cold years all of these clusters were killed, as were those 

 naturally on the trees. After the mild winter they all hatched com- 

 pletely. 



Those clusters in the inverted jars received a considerable amount 

 of protection, as they were in no way affected by storms. Low tem- 

 perature could act upon them freelv and to a certain extent the at- 

 mospheric moisture could do so, for the jars were open at the bottom, 

 allowing air to ascend into them when it became warm. Xo rain or 

 snow could reach them, however, and as a result they remained x^er- 

 f ectly dry duiing the entire winter, as was proved by numerous ob- 

 servations. They were therefore not frozen or covered with ice, as 

 were many of the clusters in the open. 



These clusters were only exposed to temperature and atmospheric 

 moisture. It has been shown already that humidity can play very 

 little, if any, part in killing the eggs: therefore it may be considered 

 that if these eggs were killed temperature must have been responsible. 

 To corroborate this conclusion all eggs exposed in this manner failed 

 to hatch after the cold winters, but hatched perfectly after the mild 

 one. 



Experiments in natural protection were suggested by notes taken 

 in connection with the " observation point " investigations, as has 

 already been noted. It was found that those placed close to the 

 ground at nonhatch points, whether in cavities, under roots, or in 

 the open, hatched completely, while those high up were killed. At 

 first sight snow appeared to be the protecting factor: and this sup- 

 position was borne out later by actual observation, though it was 

 some time before all variations could be reconciled with this theory. 

 To afford protection the snow had to cover the clusters during every 

 severe cold spell, which it did not do because of the countless varia- 

 tions in its depth, and it was only after a long series of observations 

 in the woods that a true appreciation of the variableness of this 

 factor became apparent. Depth even immediately after the cessa- 

 tion of a .storm varied enormously, particularly if the snow was light, 

 for every breath of air induced drifting. Many times also the eddy- 

 ing of the wind around the tree trunks left the snow piled against one 

 side and blown away from the other. The resulting depression 

 served to expose some clusters while others remained covered, a fact 

 which explains why clusters close to the ground were killed and 

 those much higher hatched. 



A close following of the snow history of a section during the winter 

 showed great fluctuations in depth, when measured on the trunk of 

 a tree small enough to be unaffected by the wind eddies mentioned 

 above. At the end of a storm the snow would be piled to a certain 

 height on the tree: then gradually settling would take jolace. until 

 after the lapse of a few days there would be several inches difference 



