Mosses and Lichens 



delicate leaf-green bearing cells from the fierce heat of the sun, 

 and for providing a means by which water may be quickly trans- 

 ferred to all parts of the plants. 



ctU. 



Perforation. 



Leucobryum vulgare. Model to show structure. 



The walls of these large colourless cells are very thin and are 

 punctured with small holes which communicate with the holes 

 of adjacent cells, so that the moment the plants are moistened, 

 the cells fill with water by capillary attraction. The large cells 

 when filled with water serve as reservoirs to the adjacent small 

 cells, making it possible for the leaf-green to do its work of 

 assimilating plant food. The greater transparency of the water- 

 filled cells makes the leaf-green of the small 

 cells more apparent from the exterior and gives 

 the plants their deeper hue, when wet. 



Dry spore- 

 Empty case to show 

 spore-case, swollen base. 



Spore-case. 



Leucobryum vulgare. 



162 



Leaf. 



