400 



HOW CROPS GRO\V. 



A 



surrounded by a compacter epidermis. Osmose takes 

 place in the epidermis with such energy as not only to 

 distend to its utmost the cell-tissue, but to cause the 

 water of the cells to filter through their walls, and thus 

 gain access to the ducts. The latter are formed in young 

 cambial tissue, and, when new, are very delicate in their 

 walls. 



Fig. 69 represents a simple apparatus by Sachs for 

 imitating the supposed mechanism and process of Eoot- 

 action. In the Fig., g g represents a short, wide, open 

 glass tube ; at a, the tube is tied over and se- 

 curely closed by a piece of pig's bladder ; it is then 

 filled with solution of sugar, and the other end, 

 b, is closed in similar manner by a piece of parch- 

 ment-paper (p. 59). Finally a cap of India-rub- 

 ber, K, into whose neck a narrow, bent glass 

 tube, r, is fixed, is tied on over b. (These join- 

 ings must be made very carefully and firmly.) 

 The space within r K is left empty of liquid, and 

 r the combination is placed in a vessel of water, as 

 in the figure. C represents a root-cell whose 



exterior wall (cuticle), 

 a, is less penetrable 

 under pressure than its 

 interior, b; r corres- 

 ponds to a duct of vas- 

 cular tissue, and the 

 surrounding water 

 takes the place of that 

 Fig. 69. existing in the pores of 



the soil. The water shortly penetrates the cell, C, dis- 

 tends the previously flabby membranes, under the accu- 

 mulating tension filters through b into r, and rises in 

 the tube ; where in Sachs's experiment it attained a 

 height of 4 or 5 inches in 24 to 48 hours, the tube, r, 

 being about 5 millimeters wide and the area of b, 700 sq. 



