134 EXPERIMENTS WITH PLANTS 



feet on a side) , which were thoroughly explored by the 

 roots, and assuming each cubic inch of earth to contain 

 only one linear inch of root. The entire root -system 

 of a Squash vine was found by actual measurement to 

 be over fifteen miles in length (not counting root- 

 hairs), and of this length the major part must have 

 been produced at the rate of 1,000 feet per day. 



The spread of the root is, in general, about the 

 same as the spread of the branches. Thus the "feed- 

 ing roots " (the fine, branching roots which do most of 

 the absorbing) of a tree are largely located beneath 

 the tips of the branches where the drip of the rain 

 and dew falls directly upon them; and the same is 

 true to a great extent of shrubs and herbaceous plants. 

 With these general facts in mind, it will be of interest 

 to investigate a few special cases, especially of trees 

 or crops common in your region. It will also be of 

 interest to examine the behavior of the roots of potted 

 plants. 



As a rule, the roots of ordinary crops do not pene- 

 trate the soil to a depth of more than three or four 

 feet, but in dry regions they may penetrate ten or 

 twelve feet (or more) into the soil in the search for 

 moisture; in consequence of this they are enabled to 

 withstand long periods of drought. Alfalfa grown in 

 dry soil may penetrate more than twice as deep as 

 this. Some crops. Grasses, etc., are known as "sur- 

 face feeders." Such are often grown in orchards, etc., 



