PICTURESQUE EXPERIMENTS 2 1 1 



We all know that in plants — from the smallest 

 weed to the giant trees of America — there flows a 

 stream of water from the root to the topmost leaf. 

 Nevertheless, it is an experience to have ocular 

 proof of this life-giving current. A branch of 

 laurel is so arranged that it has to suck up the 

 water it needs through a coarse thermometer tube, 

 dipping into a beaker. The laurel does not wither, 

 and we know therefore that it is continuously 

 supplied with water. If the beaker is removed we 

 shall see the absorption, for the thermometer tube 

 does not remain full of water ; a minute column of 

 air is seen at its lower end which rapidl}^ increases 

 in size, and finally when the tube is emptied of its 

 water-content, bubbles of air escape one after 

 another into the larger tube, which contains the 

 cut end of the branch. This, the simplest possible 

 experiment, is nevertheless a vivid ocular proof of 

 the laurel's power of absorbing water. It can be 

 shown that the sucking power of the branch depends 

 on its leaves, for if these are removed the rate of the 

 current is very greatly diminished. It can also be 

 proved that it depends on some quality of the leaf 

 surface, for if a new specimen is taken, and if the 

 lower sides of its leaves are rubbed with vaseline, 

 the rate of absorption \vi\\ be seen to diminish very 

 greatly. Greasing the upper surface of the leaves 

 does not produce this result, and when we examine 

 the two surfaces it is found that the lower one is 

 riddled with innumerable microscopic holes (sto- 

 mata), while the upper side of the leaf has no such 

 apertures. The stomata in fact are the arbiters of 

 what shall pass in or out of the body of the leaf ; 



