THE GROAVTH OF THE PLANT 95 



Ittfereiice. — Roots grx^w towards moktui«. The 

 afetractiou that w-j\ter possesses for the rv>ot is sufiBcienLt 

 to overw>iue its natural tendency to downnrard irrvnvih. 



The t^ponse produced by the preseuee of moisture 

 on the durevtiou of growth of the root is lermeii Hydro- 

 tropism. Boots ai« said to be j is ; r • ir'y hi/drotropie. 



The glass-fironted box made for Experiment r>8 o;m 

 be vised to show Terv prettily the direction of growth 

 tdkeu by each part of a sixxiliug. 



EXPBRIMEST Ol 



Aim. — To show olearlv the direction of growth taken 

 by all the parts of a seeilling bean. 



Method.— Thrtje or four moad-bean set^s are planted 

 in the gL-iss-fironted Ix^x used in Experiment oS. The 

 beans are arraugerl so that the radide in each c;\so is 

 oloso to the gla^ and yK>:n:s downwards. 



Thrwe dir>fecive forvvs, .^ has ahead j been seen, act 

 on the rtH^l of the developing serxlling. One of these 

 toivvs pulls the rv»ot ver- 

 tioallr downwards : the 

 other two draw ii awaj 

 from the glass towards 

 darkness and the luois- 

 tur? of the soiL As a p^,,, 

 result the root srrv^ws yrfi fi^^ 

 ohBquely in a ditwlion «*>«««^*«** 

 which :s the r«sidtant 

 of the three forws that act upon it. This is shown 

 gnphieally iu the figure. 



It is thus seen that the roots can W made to gTv>w 

 ckvfe to the s;lass by tikini: the box forward so that 

 the plane in which tlie^ gl.asslios is that of :he resultant 

 dir^^ion :ak«i by the root. 



It is ;Hivis.«Ke to eoTer tke glass with a pkee of 

 bkck paper. Thus, by reducing" the amount of %ht 



/\rfrntef«T 



