28 THE BIOLOGY OF FLOWERING PLANTS 



besides a very thick bunch of lateral roots, from the eight 

 main roots, which extended every way in a hemisphere 

 about nine inches from the stem and main roots. 



" In order to get an estimate of the length of all the 

 roots I took one of the main roots with its laterals and 

 measured and weighed them ; and then weighed the other 

 seven roots with their laterals, by which means I found the 

 sum of the length of all the roots to be no less than 1448 feet. 



" And supposing the periphery of thin roots at a medium 

 to be 0*13 1 of an inch, then their surface will be 2276 square 

 inches, or 15 "88 square feet ; that is equal to 0*4 of the 

 surface of the plant above ground." — This estimate has 

 the added interest that it is one of the first examples of 

 the application of quantitative methods to physiological 

 problems. 



Nobbe, in the paper quoted above, measured the numbers 

 and the total lengths of the root systems of the one-year 

 seedlings of the three common conifers, and compares the 

 effectiveness of the root system of the pine, with over 3000 

 roots having a combined length of 1198 cm., with that of 

 the fir, which has only 134 roots in all 99 cm. long. Such 

 differences throw light on the ability of the pine to thrive 

 in diy barren soils. The root systems of our broad- 

 leaved trees are usually rather shallow, but may extend 

 horizontally for great distances ; that of the elm has been 

 recorded with a spread of more than 50 feet. Sachs 

 reckoned the volume of soil exploited by the roots of a 

 good-sized sunflower to be a cubic metre. 



Interest has always attached to the depth to which roots 

 penetrate. Our native plants, living usually in well-watered 

 and rather shallow soils, are seldom very deep rooted. 

 Hannig (19 12) found the roots of Convolvulus arvensis 

 penetrating to the unusual depth of 2-2*30 m. On deep 

 peat the roots of sedges and other plants may attain 

 depths of 6 feet and more. There is at present little 

 precise information about the root systems of our native 

 plants. 



The most exact and extensive investigation yet made 



