MICHIGAN ACADEMY OF SCIENCE. 61 



the right quantity of material to prochu-e the niaximum al^sorptioii and the 

 mininium.loss. Moreover the growth of the root in length l)rings it about 

 that these new root hairs are in a new portion of the soil. 

 - At the other end of the machine involved in transfer, are the guard cells 

 of the stomata whose office a]:)pears to be mainly to regulate the size of the 

 opening between them, and thus control the intake ami the outflow of air. 

 This outgoing air is laden with water vapor, and this is the water of the soil 

 relieved of its small amount of inorganic matter. 



Now for the return system. In the living green cells of the leaf the carbo- 

 hydrates and other similar compounds are organized out of the inorganic 

 materials, carbon dioxide and water, and these substances, to be transferred, 

 must be in a liquid form, and in order that this liquid may pass from cell to 

 cell by osmotic action it must be an aqueous solution, not an oil or a colloidal 

 substance. The chief force, so far as is known, in causing transfer from cell 

 to cell, is osmotic activit3^ The condition of the cell sap content is the im- 

 portant factor determining whether the flow be fast or slow, positive or nega- 

 tive. Soon, however, even in the small veins of leaves, the organic liquid is 

 forced into a system of tubes, which might be compared to a number of short 

 pieces of gas-pipe, end to end, but with a porous plate or sieve across at the 

 joints. Through these tubes colloidal or other material may go but slowly. 

 Through the lateral walls of these tubes much material is pressed out into 

 neighboring — very elongated — cells. These are (ialled companion cells, and 

 they aid very materially in the process of transfer. While these substances 

 are being transported from the leaf in the direction of the root, much of them 

 is taken up and used by the living tissue on the way; and often some of them 

 are stored here and there by the wayside. But a large amount must reach 

 the roots to furnish a supply of food. It must even reach the root hairs, 

 because these are dependent upon such matter for a supj^ly of food. The 

 soil water is absolutely of no direct value as a food supply. 



The second plant, the pine, differs from the maple in that it has no tubes 

 in its upward system. The current is carried through the wood cells, from 

 one to another, very readily because these cells have in places very large 

 openings from one to another where the}^ lie adjacent to the medullary ray 

 cells, which cells also have large openings to correspond with those of the 

 wood cells. This makes a tolerably direct course for the water upward through 

 the stem. Such structures are peculiar to the pines and other conifers. But 

 for the downward conducting apparatus they have a well defined sys- 

 tem of tubes in both wood and bark. Through these tubes is con- 

 ducted the organized material, part of which is in the form of resin. At cer- 

 tain times of the year much starch is found in the bark of such trees, but later 

 there is little starch and much gum or resin. This gum is made from other 

 organized matter and is secreted in large resin glaads in the bark. It is con- 

 ducted from these resin glands through living cells of cortex and of medullary 

 ray into the resin ducts of the wood. The downward current in conifers there- 

 fore differs from that of the maple in that some of the organized material 

 passes dow^n through the wood as well as through the bark. The material 

 from the glands of the l:)ark passes through the living cells of the medullary 

 rays until connection is made with a resin duct in the wood, and from that 

 downward to other medullary rays, w^here it may be conducted outward 

 toward the bark again. Besides this resin apparatus of the conifers, they 

 have a sieve tube system similar to that of the maple. 



In a sunflower the systems are practically the same as that of the maple 

 excepting that as the sunflower is an annual and the maple a woody perennila, 



