THE STRUCTURE AND FUNCTION OF HIGHER PLANTS 7 1 



spherical, again shaped like a narrow chest. If some botanist were here to 

 lecture as we pass the various factory units, he could tell of cells which 

 combine sugar with substances brought up from the roots, thus forming 

 material from which to biiild protoplasm; of cells which make resin; of 

 several sorts of cells which form channels for carrying sugar and starch 

 and proteins and water and carbon dioxide. Further information he could 

 not furnish. Which cells govern the repairs of an injured bit of the water- 

 proof coat of a leaf? Whence issue the orders for sending to the stem more 

 sugar, or for receiving more nitrogen and sulphur to increase the stock of 

 proteins? What cells direct the ducts of a given area to furnish more water 

 or to clear away more oxygen? In short, where reside the instincts that 

 direct the cooperation of the two or three million organisms which live 

 between base and tip of one needle? When science can answer, it will have 

 made the first step toward understanding a tree. 



We can not linger for any more speculations of this sort, because a 

 long journey lies ahead. Slip into this tunnel which carries a stream of 

 sugar solution to the base of the cluster of needles. What! You are afraid 

 of drowning? But there is no way to move about in a tree except through 

 these ducts that carry water up and dissolved food down. Be courageous. 

 You have now entered into the life of the tree and will find that you can 

 breathe in its sap. Have no fear. Dive in. 



The current is swift enough to be rather terrifying, but you will grow 

 accustomed to the speed. It feels Hke ten miles an hour, and it is that fast 

 if you measure by the sort of standard you used in your human state. Then 

 you had a unit of length called a "mile," which was about nineteen hundred 

 times your height; when you traveled nineteen thousand times your height 

 in sixty minutes you said you were going "ten miles an hour." You are 

 now moving at a rate about nineteen hundred times your height in one 

 hour. The rate will increase somewhat after we reach a large branch. Just 

 what the speed of currents is in this pine I can not learn, but in some fleshy 

 plants the movement of sap is, at times, as fast as five hundred and fifty 

 miles an hour. So we are guessing our present rate very conservatively. 

 As human beings measure distance, we are about ru'o inches from the base 

 of the cluster of needles; as that distance is measured by tree tourists, it 

 is seven miles; hence we shall be forty minutes in reaching the stem. 



Perhaps I had best remind you once more, at the risk of repeating too 

 much, that this smooth, round tunnel through which we pass is not an 

 excavation. It is not even a space left vacant by the architects of the needle. 

 No, each section of the tunnel was originally a cell, which removed all of 

 of itself except the sheath, broke down its end walls, and joined itself to the 

 sheaths at either end, thus forming a continuous duct. All space in a tree, 

 everything in a tree, was designed and made by cells. 



As we swirl along and you grow accustomed to the fish-like way of 

 breathing, you notice that there are fewer factory cells and that we are 



