IX] EXPERIENCES IN THE LABYRINTH 91 



The interchange is also facilitated by the continuity 

 of the system of intercellular spaces, not only throughout 

 the leaf, but throughout the whole plant, and with the 

 external world by means of the apertures in the epidermis, 

 known as stomata (Fig. 26) and to be described shortly. 



Let us imagine, for the sake of illustration, that there 

 existed some minute intelligent being, with sufficient 

 activity to wander through the enormous labyrinths of 

 intercellular passages, and try to figure to ourselves what 

 experiences he would encounter. He must be supposed 

 to be small enough to enter one of the stomatal apertures, 

 and able to wander about freely in the intercellular pas- 

 sages (see Fig. 26), and to have all his senses attuned to 

 the minute scale of his environment. The kind of ex- 

 periences he would have would be somewhat as follows. 



During the night the passages would be charged with 

 water-vapour to excess, and if the temperature was low 

 the cell -walls lining the passages would probably be 

 dripping wet, the quantities of water exuded depending 

 on various circumstances, but being especially abundant on 

 a cool night after a hot moist day. In the darkness, more- 

 over, our hypothetical traveller in the maze of intercellular 

 tunnels would find difficulties in breathing ; for every cell 

 would be pouring out small quantities of carbon-dioxide as 

 the result of its own respiration of the oxygen of the air in 

 the passages, and in certain states of the atmosphere we 

 may picture the victim of the labyrinth having to keep 

 near one of the stomata as his only chance of obtaining 

 fresh air. At this orifice there would be draughts, moist 

 air laden with carbon-dioxide passing outwards and drier 

 fresh air pressing inward, the rate and quantity of flow 

 depending on the differences of temperature, vapour- 

 tension, &c., in- and out-side the leaf. 



As the sun rose and illuminated the leaf, our traveller 



