228 



A TEXTBOOK OF BOTANY 



[Cn. V, 4 



thus, whenever a solution and water , or two solutions of 

 different strengths, are separated by a membrane which they 



can wet, there is always a 

 movement from the weaker to 

 the stronger at a rate propor- 

 tional to the difference in 

 strength. 



In the foregoing experiment, 

 though the solution rises in 

 the tube, some also escapes 

 into the water, as shown by 

 its color when molasses is 

 used. From the root hairs, 

 however, no sugar escapes to 

 the soil. When we seek a 

 structural reason for this dif- 

 ference, we find that the root 

 hair possesses a protoplasmic 

 lining, which has no counter- 

 part in the tube. It is, how- 

 ever, entirely possible to make 

 up from certain common 

 chemicals, and supply to the 

 parchment tube, a lining which 

 in this respect acts like the 

 protoplasm, viz. it permits 

 water to enter, but no sugar to 

 pass out; and such " artificial 

 cells" are often constructed in 

 botanical laboratories. Thus 

 .<e that membranes exist 



The larger jar contains water, the which permit both water and 

 ;ube inside is parchment paper, and .,. n na ^PFTJMVAPITF 

 the dark liquid is molasses. When SU ^ ar tO P aSS ERMEABLE 



this liquid has risen to the top of membranes), while others per- 

 ^r A'o^t^ mit only water to pass (SEMI- 



cock of the reservoir-funnel. PERMEABLE membranes). This 



