310 LIFE : OUTLINES OF GENERAL BIOLOGY 



course, ever saltening from its incoming rivers), may correspond 

 to the time of their emergence from the sea — may here be suggestive. 

 For can the somewhat kindred speculation be avoided, that the 

 gradual extinction of old forms, and the appearance of new types, 

 and these respectively of plant and animal life, may have been 

 influenced by these atmospheric changes? No doubt the persistence 

 of a good many ancient types in both kingdoms seems an objection ; 

 yet may not these be but survivors through a little more respiratory 

 adaptiveness ? Difficult though this problem be, experiment has 

 long shown the advantage to vegetative growth through consider- 

 able increases of CO2, and experimental embryologists are applying 

 both kindred and converse atmospheric changes to animal-life also; 

 so why not continue such questionings, and see if in time we can 

 interpret them more widely? 



THE TRANSPIRATION CURRENT.— How far we would travel 

 to see water rising high into the air and then falling in green spray. 

 Yet few of us have to travel far; for, as Ruskin long ago said, the 

 tree is a green fountain, and with the further marvel that its waters 

 do not fall. The birches and beeches, the horse-chestnuts and syca- 

 mores, the larches and all the wood — what assemblage of life's 

 fountains ! There is no doubt that water has to rise to the topmost 

 branches of these lofty trees and even to three or four hundred feet 

 in the great Australian eucalyptus, if the buds of last year's 

 making are to be unfolded. No doubt some water is stored in the 

 stem of the tree, but that serves only for a beginning; the bulk 

 of the water has to be raised out of the soil. How is this done? 

 Moreover, apart from the swelling of cells that bursts the imprison- 

 ing bud-scales, there is the rapid growth of the potential leaves, 

 which spread themselves out to the sunshine. Everywhere in 

 growing tissue there is the intricate process of cell-division — in 

 its way more wonderful than the making of a double star. All 

 the new cells have to be fed, and this means making abundant car- 

 bohydrates and proteins, and so forth. In other words, there has to 

 be photosynthesis. 



Li\'ing matter or protoplasm contains at least seventy-five per 

 cent, of water, so that its growth and increase demand much water. 

 The food-making photosynthesis also requires water as one of its 

 raw materials. Whenever the growing leaves expand in the genial 

 air there is not only evaporation, but active transpiration, and this 

 is the largest demand of all. Hence, then, it is that the fountain docs 

 not fall. 



rivcryone who knows the whistle that the herdboy made knows 

 how easy it is, with moistenings and tappings, to slip off the rind of 

 a three-inch piece of a young branch. The rind slips off from the 

 wood by the ready rupture of the "cambium layer", yielding and 



