Proceedings of the 



"chemical changes in those fluids. Each of these topics requires a few 

 remarks, and first I shall speak of the way in which the roots obtain water 

 ■from the soil, holding food elements in solution. (1.) The water is derived 

 •from rain and dew. These rains and dews collect ammonia and carbonic 

 iacid from the atmosphere, and carry them down into the earth, (2.) 

 Earthy phosphates, silicates, and other matters essential for plants exist in 

 the earth, but mostly in an insoluble state, and therefore not ayailable for 

 growing plants. (3.) The ammonia and carbonic acid brought into the soil 

 by the rain and dew have the power of rendering these insoluble silicates 

 &nd phosphates soluble in water. (4.) Solutions of silicates, earthy 

 phosphates, and salts of ammonia filtering through ordinary soil deposit 

 the matters they contain in solution on the surface of the particles com- 

 posing that soil, and allow the water to pass on in a purified state. (5.) 

 The rootlets of plants penetrating between the particles of soil are at one 

 and the same time brought into contact with the matters thus deposited 

 (which constitute the nourishment of plants) and with water containing 

 carbonic acid, by which that matter is made soluble. (6.) The 

 solution so made, and so brought into contact with the rootlets, is absorbed 

 by them and conveyed into the plants as sap. The amount of water supplied 

 to plants has much influence on the rate of their growth, on the tissues 

 they develop, and on their general habit and strength. An abundant supply 

 of water produces weak succulent stems, abounding in leaves, but 

 deficient in fruit. A dry season produces the best fruit and the 

 richest harvests; old and dry seeds of melons and cucumbers 

 grow less vigorously than recent ones, but bear better crops of fruit ; 

 shrivelled seeds of stocks produce double flowers, while plump and moist 

 seeds grow plants bearing only single flowers. The benefit of transplanting 

 depends in part on the fact that some of the roots die, and by their decay 

 extricate carbonic acid, which, by rendering soluble the otherwise insoluble 

 constituents of the soil, accumulates nourishment in the fittest state for 

 absorption by the newly formed rootlets, at the very spot where it is 

 required. After its absorption by the roots the sap ascends through the 

 stem to the leaves. In its course it is subject to various movements, and 

 undergoes different modifications of its composition. In all of these 

 changes water forms an important agent. It gives to the sap that degree 

 of fluidity which enables it to rise with the necessary rapidity in the 

 capillary tubes of the stem ; to pass by slower degrees from cell to cell, by 

 virtue of the permeability of the ceU membrane ; to produce the varieties 

 of cell circulation, cyclosis, and rotation ; and to assist in the elimination 

 and transport of the various secretions. To show the need of this water- 

 given fluidity to the sap, I need only mention that the rate of its ascent has 

 been ascertained to be 40 inches per hour in the cherry laurel, and even as 

 much as 15 inches per minute in the sun-flower. The slower passage of the 

 sap from cell to cell imphes not only the permeability of the cell wall to 

 vratery fluids, but also, as I imagine, some special relationship or adaptation 

 in the cell membrane to this particular purpose. I can neither explain 



