228 



A TEXTBOOK OF BOTANY 



[Ch. 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 



Fig. 168 -An osmoscope, for we gee that membranes exist 

 the demonstration of osmosis ; X &. 



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

 ;ube inside is parchment paper and gr to (PERMEABLE 



the dark liquid is molasses. When ° • i 



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



the open tube it can be dropped Jt j water to ( gEMI _ 



back to level by opening the stop- J \ mu • 



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



