1895 THE MICROSCOPE. 1T9 



at the two corners towards the pore, which is provided 

 with projecting ridges. 



Each stomata opens into a large intercellular space 

 called the air chamber (figs. 5 and 8, t). The air chambers 

 communicate with the intercellular spaces of the leaf and 

 through them with those of the whole plant. The stomata 

 then are the pores by which the intercellular passages of 

 the Avhole plant open into the external atmosphere. 



The stomata have the power of opening and closing. 

 As a rule they open under the influence of light and 

 warmth and close when it is dark and cold, or they open 

 when the guard cells are distended and close when they 

 are relaxed. To prove this take a s*ection of the amaryl- 

 lis, which has a long stomata, from a living plant and 

 place it in Avater under the microscope. The guard-cells 

 will be seen to open more and more and the pore between 

 them opens to its full extent (fig. 10). Now replace the 

 water by a solution of salt — a strength of two per cent 

 is sufficient. The curvature of the guard-cells now dimin- 

 ishes and as they straighten themselves the pore between 

 them closes (fig. 9). The pure water is absorbed into the 

 guard-cells by the denser cap-cells so their turgidity is 

 increased, and the comparatively dense salt solution 

 withdraws water from the guard-cells and thus they tend 

 to collapse. 



That the guard-cells become curved as they distend is 

 due to the ridges by which each cell is strengthened ^on 

 the side towards the pore. This side is more rigid than 

 the other and so offers greater resistance to stretching 

 when water is taken up. Hence the more inflated the 

 guard-cells are, the more convex they become on the ex- 

 terior and the more concave on the side next the j)ore, 

 thus making the space between the two cells larger. But 

 when the water is withdrawn the reverse happens. 



To make a permanent mount first strip off the epider- 

 mis, and to prevent it from curling, spread it out quickly 



