354 THE PHILIPPINE islands. 



The mass in this case appeared never to have had any crater. 

 It rose with steep walls directly from the soil formerly covered 

 with vegetation, which it had destroyed. It appeared as if the 

 trachytic lava had issued from a central cavity, and boiled over 

 as it were, till it set into the form of the dome. 



The ground around the crater was still almost bare of vege- 

 tation, but some plants were beginning to colonize the denuded 

 soil, strongly impregnated as it was with various volcanic 

 chemical products. Three species of ferns, as first colonists, 

 grew as isolated plants here and there : and along the courses 

 of two small streams fed by hot springs, issuing from the base 

 of the volcano, where the poisoned ground was constantly 

 washed, a good deal of vegetation was to be found, amongst 

 which were several sedges and grasses, and a rush. 



About the mouths of cavities from which hot gases were 

 slowly being exhaled, a moss was found growing in great abun- 

 dance, with several lowly organised Cryptogams; the whole being 

 confined to the spot occupied by these fumeroles and forming 

 green patches in the midst of the surrounding entirely bare rock. 



The hot strearis were full of green algae, and as these streams, 

 being very small became cooler and cooler from their source 

 downwards, I was able to determine the temperature at which 

 the algae commenced to flourish. 



At the source of one of these streams, as it issued from 

 beneath the volcano, the water had a temperature of i45°"2 F., 

 and was thus too hot to be borne by the hand. Here there 

 were no algte at all growing in the water. There were, however, 

 small green patches on stones projecting out of the bed of the 

 stream into the air, and also along the margins of the stream 

 where they were not bathed by the hot water itself, but only 

 soaked up the moisture and received the spray occasionally. 



At a distance of a few yards lower down, in a little side-pool 

 fed by the stream, abundance of algje were growing, but the 

 pool had a temperature of only ioi°'5 F., though the stream 

 which fed it constantly was at 122° F. 



Lower down again, algae were growing in the middle of the 

 stream, in water at ii3°'5 F., and this seems thus to be the 

 limit of temperature at which the particular algae gathered, will 

 flourish in water impregnated with a certain amount of salts in 

 solution. No doubt the amount of salts present has a limiting 

 effect as well as the temperature. 



Oscillatorice. have been observed growing in water, at a much 

 higher temperature, even 178° to 185° F.* The fact is interest- 

 ing, as showing that green algae of some considerable coni- 



* See W. T. Thiselton Dyer, F.L.S., etc. " Proc. Linn. Soc, Bot.," VoL 

 XIV., p. 327, Also pp. 32 and 331 of present work. 



