410 A NATUKALIST ON THE "CHALLENGER." 



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 streams were full of green algse, 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 algse commenced to flourish. 



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

 beneath the volcano, the water had a temperature of 145 0, 2 F., 

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

 no algse 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 algse were growing, but the pool 

 had a temperature of only 101 o, 5 F., though the stream which 

 fed it constantly was at 122° F. 



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

 stream, in water at 113°' 5 F., and this seems thus to be the limit 

 of temperature at which the particular algse 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. 



Oscillator ice, 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 algse of some considerable complexity 

 may have commenced life on the earth in its early history, before 

 the water on its surface had anywhere cooled down to a tem- 

 perature sufficient to be borne by the human hand, and which 



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

 Vol. XIV. p. 327. Also pp. 36 and 383 of present work. 



