99 



where the trunk is cleft in large branches; many of these holes are never filled with 

 rainwater because it immediately sinks down into the ground, or into the decaying 

 wood; in very dry summers the holes hold no water or only very small quantities. 

 In some of them, more especially those in which the bottom itself is of wood, and 

 not part of the ground, the rainwater can be retained for months, more especially 

 when a little rain now and 

 then can replace the loss by 

 evaporation. In these holes 

 the bottom is almost always 

 covered with decaying vegeta- 

 tion, more especially leaves, 

 which in its deepest layer 

 form a black humus. The 

 water is dark-brown and of 

 an extremely foul odour, 

 smells strongly of hydrosul- 

 phuric acid; the volumina of 

 water are often less than a 

 deciliter, and never more than 

 from three to four liters. In 

 autumn the holes are filled 

 with leaves; from December 

 to May the contents of the 

 holes can with more accuracy 

 be described as moist leaves, 

 than as clear water; for more 

 than three months the whole 

 mass is frozen into a brown 

 ice; at the bottom of tlie holes 

 I have however almost al- 

 ways found a layer of frost- 

 free, black humus. The tem- 

 perature of the water is re- 

 markably constant during the whole summer and always rather low; even on hot 

 days, where the ponds have temperatures of about twenty-five Celsius, the holes 

 rarely have more than about twelve degrees, and probably never more than fifteen. 

 This is due to the fact that the water in the tree-holes hardly ever receives a single 

 sunbeam. Though the water has a disagreeable smell, it is commonly clear, and 

 most closely resembles fresh urine. The bad smell is strongest when the bottom is 

 stirred up. What certainly contributes to the bad quality of the water is the huge 

 mass of drowned animals which first cover the surface of the water and later on sink to 

 the bottom and decompose. Every heavy shower carries large quantities of animal- 



13* 



Textfig. 11. Hole in a trunk. Finlaya geniculata and Anopheles 



nigripes. 



