MICHIGAN ACADEMY OF SCIENCE. 57 



THE WATER SYSTEMS IN PLANTS. 



J. B. D.\NDENO. 



The importance of water in the physiological ojDerations of plant life, in 

 regard to both the vital and the physical sides, can hardly be of much less 

 consequence than that of air. That water is of extremely high importance 

 in plant economy, is fairly well known. Perhaps, in a general way, it is better 

 understood on account of its tangibility, than are the air relations. But there 

 is much that is intricate and difficult about the actual conditions in connec- 

 tion with the water systems. To point out in a general way the fundamental 

 ]irinci])les involved in the water relations is the object of this ])aper. 



It need not be saiii that w^ater is an essential substance in the welfare of 

 plants. All organisms require it. The earliest forms of both plants and 

 animals were aquatic, and consequently required it in abundance. In such 

 organisms the water systems were comparatively sim])le because the organ- 

 isms in all stages of their lives were actually immersed in it. But as these 

 organisms began to adopt a semi-aquatic habit, or a land habit, their in- 

 ternal and external structures became modified to suit the changing con- 

 ditions. However, no matter whether the plant lives immersed in water or 

 in air, water is essential to the vital processes. There are some instances 

 relating to plants in desert regions and to such portions of plants as seeds, 

 which might seem to indicate that water was not absolutely essential, though 

 at first sight they might seem to be. In such cases the organism is able 

 to undergo a dormant existence with only a very small quantity of water. 

 This small ciuantity, however, is quite essential. 



The structures which have to do with the intake of water into organisms 

 in general are: The epidermal cell wall, protoplasmic membrane (which lies 

 immediately within the cell wall and ordinarily pressed firmly against it), the 

 protoplasm itself, and tissues of several kinds. Not less important, perhaps, 

 are those parts which are especially adapted to retaining water which has 

 already been absorbed. These parts assume a great variety of forms both 

 as to tissues and to epidermal outgrowths. In connection with these should 

 be mentioned such forces as have directly to do with the transfer of water 

 from place to place in a plant, or from cell to cell. In close connection with 

 these should be included such mechanisms as have to do with the liberation 

 of water to the surrounding medium. To summarize, then, we present those 

 structures which are concerned in absorbing, in transferring, in retaining and 

 in giving off water. 



In regard to plants which lie immersed in water or are floating upon it, the 

 water system is comparatively simple, involving chiefly a physical attraction 

 which has been generally termed osmosis. This phenomenon of osmosis is 

 theoreticalh^ not difficult to explain, but unfortunately, there are diametric- 

 ally opposed views with respect to the theories advanced to explain it. It 

 would not be worth while to go farther into an explanation of the process of 

 osmosis, than to state that there are tliree essential factors concerned with 

 the process: (1) a premiable or semi-premiable membrane which is exten- 

 sible and elastic, and therefore capable of reducing the size of, or of enlarg- 

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