MICHIGAN ACADEMY OF SCIENCE. 59 



rather well-marked tissue systems have been developed in roots, stems and 

 leaves. 



With regard to the entry of solutions into the roots, osmotic action is the 

 chief (practical!}' the only) factor; in transfer from cell to cell it is also the 

 only known factor; but this is necessarily a slow process, and one involving 

 many changes — many of them probably unnecessary — in the character of 

 the solution which entered the root. Conseciuently more direct systems 

 have been develojjed, and in the highest forms of plants this system consists 

 of a series of tubes end to end, reaching from the rootlets to the smaller 

 bran(;hes of the veins of the leaves. These tubes are modified cells with the 

 end walls gone, either wholly or in part. This system of tubes, sometimes 

 called the vascular system, develops in certain well-defined portions of the 

 plant, and in many cases they, with the accompanying cells, form what is 

 called the fibre of the plant. There are two chief types of arrangement of 

 such filjres in stems — (1) that found usually in dicots, (2) that in monocots. 

 But in roots there is a more varied arrangement. 



In the dicots, where the i)lant is an herbaceous one, these fibres form one 

 well-defined ring around the outside of the pith. The inner portion of these 

 fibres has to do with the transfer from root to leaf, and the outer portion 

 from leaf back towards the root, the one conveying unorganized material 

 and the other oj'ganized material. There are many variations from these 

 two general plans, but these details can not be dealt with here excepting in 

 the more important phases. 



Four different forms of higher plants may l^e considered as representing 

 in a general way the peculiarities of the water systems of such plants: (1) 

 a sugar maple tree, (2) a coniferous tree, e. g., the white pine, (.3) an aniiual 

 plant of the dicot.tyi)e, e. g., the sunflower, (4) an annual monocot, e. g., 

 corn. 



The sugar maple as representing a type of Avoody dicot possesses a system 

 which, in a general way, may be outlined as follows: The root hair absorbs, 

 by osmotic attraction, water from the soil, and this water is passed on from 

 cell to cell through the softer tissue of the root until it is pressed out of the 

 cell adjoining the vessels (tubes of considerable length) into the vessels them- 

 selves. These vessels are more or less continuous through the smaller root- 

 lets into the larger ones, then into the roots and up into stem and leaf 

 petiole, into the ultimate veins of the leaf where it is removed b}^ osmotic 

 activities into the living active cells of the leaves. Of course it is cjuite prob- 

 a])le that here and there much of the water is removed from the vessels by 

 the tissues alongside, as the water goes on in its course from root to leaf. 

 These tissues are supplied with water from this source. Openings in the 

 walls of the vessels favor this process very materially. This water as it 

 passes from root to leaf is .practically soil water, and is therefore devoid of 

 any organic food. 



The forces which contribute towards this ascent of water through the ves- 

 sels are, capillary action, the force of evaporation in the leaves, inhibition of 

 cell wall, root pressure, atmospheric pressure, activities of the living active 

 cells here and there throughout the tissues, air bubbles in the conducting 

 A^essels, osmotic activities in living cells. Whether these are sufficient in 

 themselves to cause an ascent of liquid to the tops of the highest trees is a 

 matter not yet definitely settled. In fact the present view is that they are 

 insufficient. 



To trace a drop of soil water from root to leaf of the maple would therefore 

 concisely state the situation. This drop with its small amount of inorganic 



