82 



EXPERIMENTAL PLANT PHYSIOLOGY. 



bodies surrounding them which may amount to from 12 to 15 

 atmospheres. By this force roots and other fixing and ab- 

 sorbent organs are driven through the soil, and aerial organs 

 push their way upward through the air. The total amount of 

 energy used in the performance of external work during the 

 lifetime of the plant is very great. The spore-bearing cap of a 

 Mushroom has been known to lift a weight of 160 kilograms. 

 A root of Larch 30 cm. in diameter has lifted a stone 1600 

 kilograms in weight, while a root of a germinating Bean has 

 exerted a lateral pressure on the soil amounting to 1.5-4 kilo- 

 grams. All growing organs expand with similar force, but in 

 the examples given the form of the organ is such as to utilize 

 the force in penetrating the substratum. The growing fruit 

 of a Cucurbita is capable of exerting a pressure of several 

 FIG. 71. thousand kilograms, though it ordi- 



narily meets with no resistance. 

 EXPERIMENT in. 



POWER OF PENETRATION OF RHIZOIDS OF A 

 HEPATIC. 



If a Hepatic is placed on several folds 

 of moist filter-paper in a chamber satu- 

 rated with moisture, within forty-eight 

 hours the rhizoids will have pierced the 

 filter-paper. The holes through which the 

 rhizoids have penetrated were certainly 

 not there before. The fibrous structure 

 of the paper is so dense that a starch- 

 grain of corn, which is only two micro- 

 millimeters in diameter, cannot find its way 

 through, yet the rhizoids, which are 10 to 



micromillimeters in diameter, easily 

 Force exerted by growing " 



roots. (Mangin.) accomplish it. 



EXPERIMENT 112. 



FORCE EXERTED BY GROWING ROOTS. 



To a small upright stand attach a horizontal arm bearing a small 

 wooden pulley. Fasten a scale-pan to a cord passing over the 



