_>02 



BOTANY 



sap of some plants is so great that sugar may be profitably derived 

 from it. The sap of the North American sugar maple, for example, 

 contains i per cent of sugar, and a single tree will yield 2-3 kilos. 

 The sap of certain plants is also fermented and used as an intoxicating 

 ilrink (birch wine, palm wine, pulque, a Mexican beverage made 

 from the sap of Agave, etc.). One inflorescence of Agave will yield 

 1000 litres of sap in from four to five months. 



The bleeding which takes place on warm, sunny winter days from wounds o: 

 in trees is not duo to root-pressure, but to purely physical causes. It is 



brought about by the expansion of the 

 air- bubbles in the tracheal elements i,f 

 the wood, and may be artificially pro- 

 duced at any time in winter by warming 

 a freshly cut piece of wood ; when tin- 

 wood is allowed to cool, the air contracts 



iin( i t ne water in contact with the cut 



e .,, , , , , 



surface will be again absorbed. 



In some lianes the vessels are so wide 

 that they do not retain the water by 

 capillarity. When such stems are cut 

 drinkable water flows from them in con- 

 siderable quantity. 



2. THE COURSE OF THE WATKI: 

 IN PLANTS. In living plant-tissues 

 the cells of which require more or 

 less water for their growth and for 

 the maintenance or augmentation 

 of their turgidity, there is a con- 

 stant transfer of water from one 

 cell to another. This transfer 

 between the adjacent cells takes 

 place much too slowly to equalise 

 the great amount of water lost 

 by evaporation from the foliage 

 of a tall tree. IN ORDER TO 



TRANSKKI! THK WATER, QUICKLY 

 si, as those on the uninjured braneh ,-; ANJ) m LAR(JER QUANTITIES, FROM 

 .'. vessel containing water. Facsimile of the 



illustration in HA..F.S' V.,,,,,,1,1, Statta, 17-27. THE ROOTS TO THE LEAVES, PLANTS 



MAKE USE, NOT OF THE LIVINi; 

 PARENCHYMA, BUT OF THE WOODY PORTION OF THE VASCULAR 



BUNDLES. The woody elements which thus conduct the water have 

 no protoplasm. 



3. THE TRANSPIRATION CUJIIENT. It has long been known thai 

 the ascending transpiration current in woody plants flows solely 

 through the wood. It had been observed that plants from which 

 portions of the cortex had been removed, either purposely or acci- 



ii. 188. HAI.I:> experiment to show the ascent 

 of the sap in the wood. Although the cortex 

 has been entirely removed at Z, and the wood 

 :il, me left, the leaves of the branch b remain 



