76 TYPICAL FLOWERS OF ALPINE PASTURES 



the little heaps or accumulations of calcium carbonate 

 or chalk, which mark the position of the glands. 

 We have already shown (p. 10) that the leaves of 

 all plants have numerous but very minute pores 

 or openings, by which the atmosphere has free 

 entrance into the substance of the leaf itself, 

 and by which the gases evolved by the internal 

 mechanism of the leaf pass back to the atmo- 



a. 



FIG. VI. Section through a Chalk-gland on the edge of a Leaf 

 of a Saxifrage. 



to, the water stomata ; g, the chalk-gland ; .&., the vascular bundle of 

 the leaf. Highly magnified. 



sphere. In most plants these pores or stomata 

 can be opened and closed. The chalk-glands or 

 water stomata of the Saxifrages, on the contrary, are 

 differently constructed, and remain always open. In 

 order to prevent an undue amount of water- vapour 

 escaping from the leaves a matter of great 

 importance to plants which, like the Saxifrages, grow 

 in dry situations with but a limited supply of moisture 

 in the soil a small quantity of calcium carbonate in 



