582 THE POPULAR SCIENCE MONTHLY 



hole so charmingly described by Mrs. Austin. Every trout-fisherman 

 has seen the roots of alder and willow growing from the bank into the 

 stream. We are accustomed to having our house-sewers stopped up 

 by the roots that will grow into them, though there is much more room 

 outside. But the formative influence of water is not so obvious. Yet 

 wlien we think of the creatures, plants and animals, of arid regions and 

 of well-watered ones, we perceive certain differences. When we realize 

 that water is formed, or is the surrounding medium, in almost every 

 chemical reaction which takes place outside the living body, and in 

 every chemical reaction within the living body, its importance is evi- 

 dent enough. The shape, size, structure and covering of every animal 

 and plant are influenced by the ease with which water may be obtained 

 and held. All land animals and plants lose water from their bodies by 

 evaporation; submersed aquatics do not. Land animals and plants 

 ordinarily get water from the earth, from depressions in its surface or 

 from its soil, and only through those limited parts of their whole bodies 

 which touch the water; but aquatics can take it in through their entire 

 surface. If a land plant or animal takes in water only through its 

 roots or its alimentary canal, there must be some system for distributing 

 the water to all the parts of the body; but this is not necessary in 

 aquatics. The difl'erences in structure and form between land and 

 water organisms is, then, partly due to their relations to water. The 

 differences between the tadpole and the frog, between the submersed 

 and floating leaves of the water-buttercup, between the swimming 

 sperm of moss and fern and the wind- or insect-borne pollen of the 

 higher plants, these differences are in their relations to water, in the 

 degrees in which the formative influence of water has been unopposed 

 by other factors. 



Before turning to other formative influences, we should realize that 

 the force of gravity acts constantly, night and day, uniformly, age 

 after age, and it is impossible either to eliminate it in experiments or 

 to conceive of its operation ever being or having been interrupted in 

 nature. Water also is constant and uniform and unavoidable; for 

 until water ceases to be a necessary component of the living protoplasm 

 of the plant and animal body, until it becomes something else than 

 hydrogen and oxygen in the proportion of two to one, we can not con- 

 ceive of its being eliminated, by exclusion or substitution, in experi- 

 ment, or of its absence in nature. If water is absent, life is absent. 

 This is not true, however, of other influences, material or energetic, 

 which affect form and substance, as well as the direction of growth or 

 movement. These influences may be temporary. 



Light is not a necessary condition of active life. It comes and 

 goes, day and night. In the extreme northern mid-summer the sun 

 never sets; the winter is dark and gloomy. In spite of the lack of 

 light, however, life goes on in the winter darkness provided sufficient 



