420 BOTANICAL GAZETTE [NOVEMBER 
its heat will still further reduce the tree trunk. This process is 
continued until the tree is wholly consumed and the lava has 
filled the mold. The main flow passes on, leaving the lava trees 
behind. The result is a lava pillar or column, 15-25 ft. high, 
2-5 ft. in diameter, and often expanded or flaring at the summit, 
where the trunk branched. These so-called ‘“‘petrified trees” 
retain many evidences of their arboreal origin, and correspond 
somewhat in their mode of formation to the petrified trees of the 
west. In the Puna district, Hawaii, there are hundreds of these 
lava trees in the wake of ancient pa-hoe-hoe flows. 
4. The fourth type of reaction between lava flow and woodland 
produces deep tubes instead of columns. The flow enters the 
‘grove and fills it to a depth of perhaps 20 ft. The rapid sheathing 
around the trunks of the larger trees protects them, as in the 
former cases, from immediate destruction. The flow in this 
instance, however, does not pass on and drain itself from the grove, 
but remains and solidifies. In the course of time the trunks 
decay and leave deep tubular vertical pits in the lava. The walls 
of these tubes are often plainly marked with the impressions of 
the bark of the trees which they once contained. The tubes are 
ro in. to 5 ft. in diameter and 15-20 ft. deep. They are known as 
“tree molds,’ and are abundant on some of the old lava flows, 
particularly in the vicinity of Kilauea. 
CoLLEcGE OF Hawatt 
HoNnoLuLu 
