228 



A TEXTBOOK OF BOTANY 



[Ch. V. 4 



thus, — whenever a solution 

 different strengths, are separa 



Fig. IGS. — An i ui 

 the demonstration of osmobife , X l- 



The larger jar contains water, the 

 tube inside is parchment paper, and 

 the dark liquid is molasses. When 

 this liquid has risen to the top of 

 the open tube, it can l.>e dropped 

 back to level by opening the stop- 

 cock of the reservoir-funnel. 



and -water, or two solutions of 

 ted 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 tulje, 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 

 cliemicals, 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 

 we see that membranes exist 

 whiclt permit both water and 

 sugar to pass (permeable 

 membranes), while others per- 

 mit only water to pass (semi- 

 permeable membranes) . This 



