340 EXPERIMENTS WITH PLANTS 



approach of cold weather and rising to the surface 

 again in the spring. Such plants, as a rule, have the 

 custom of breaking up into pieces, each of which floats 

 away and becomes a separate plant. 



A very interesting experiment may be made by 

 growing the Water-hyacinth in soil instead of in water 

 and observing the modifications it undergoes. We may 

 also use the Water -polygonum for this experiment. 



196. Lower epidermis of Water-polygomim; {a) from a submerged 

 leaf, sliowing lack of stomatii, (^J from an air-leaf produced by 

 a plant growing in water. 



Water affects the size of every part of the plant 

 noticeably, as may be seen by comparing plants grown 

 in dry, sandy soil with the same species grown with 

 abundant water (e. g., the weeds which come up in a 

 garden as compared with those which grow in dry 

 spots) . 



The large wood-cells produced in the spring (spring 

 wood), as contrasted with the fall wood, are another 



iUustr^tioa of tbis (see page 247). A scion grafted on 



