6 
and it is rather difficult for plants to fasten their roots upon it 
even when there is a plentiful supply of water. Volcanic ashes 
or tufas can hold a considerable quantity of water ; but an area 
covered with tufas is necessarily plane and smooth, and here in 
a heavy rainfall, the water is likely to run off from its surface. 
What makes the matter worse for plant-seedlings is that the 
area affords no place where plants can fasten their roots and is 
too flat to have any holes or shady places for the young plants. 
When strong and dry winds prevail, such ground at once loses 
all moisture and the plants find it difficult to grow. In this sense, 
in a surface covered with jagged blocks of lava, the plants can 
best find their rooting. 
After stating so much, let us proceed to the consideration 
of the lavas of Mt. Fuji. According to Dr. T. Hirabayashi, 
some of the lavas belong to the eruption after the historical 
age, and therefore we are able to estimate their ages together 
with those of the vegetations upon them. There are seven 
streams of lava, each differing from the other, implying pre- 
historical and post-historical periods. They are as follows : — 
1) the Osawa, 2) Mishima, 3) Omiya, 4) Karasuishi, 5) Yenkyo, 
6) Aogigaliara, and 7) Hoye streams. The first four are pre- 
historical and the last three post-historical. All the lavas of 
this volcano arc basic. The Yenkyo lava is said to have erupted 
in the year 880, the Aogigaliara in the year 955, and the Hoye 
lava in the year 1707. 
Of all these lavas, the Aogigaliara which stretches over the 
Y.W. flank is the most porous and capable of supporting vege- 
tation.* The other lavas are more or less dense and compact. 
The Hoye lava consists of ashes or small particles of lava blocks, 
and is not fitted for plant growth. We, therefore, see the richest 
vegetation on the Aogigaliara side and the poorest on the Hoye 
side. 
* The ground covered with this lava is especially fitted for the growth of 
conifers. 
