192 



General Botany 



The cortical cells are essentially like those of the epidermis, 

 and the concentration of their cell sap is progressively higher 



I Cuticular transpiration [ 

 itAttnospherc 



I (^evaporation j 

 epidermal cells -^ cuticle 



Stomatal transpiration [ 

 tjltmosphere 



I (yaseous diffusion) 1 5,^^ t^^^pi^ation | 



Stomata ' ; ' 



* (Atmosphere 



I ^^'"'"'"' ^'■ff^''^^ \ (gaseous diffi^ion) 



('Tecretion oj 



iDead 

 cells 



Stomata or Icnticcls 



T (gaseous diffusion ) 

 intercellular spaces 



I (evaporation ) 



Jeod-conducfing '¥■ 

 living cortical f issues 

 I (osmosis) 



TVood parenchyma 

 pith rags 



Fig. 113. 



Sntercellular spaces 



(evaporation) 

 J\jiesophyll cells 



t (osmosis ) 

 I fi^er- conducting tissue 

 of veins I of leaf 



T (mass movement 

 I . orjloiv) 

 Heater-conducting tissue 

 qf\ petiole 



T (mass movement 

 or flow) 

 'Water-conducting tissue s 



ofstem^ (osmosis) 

 (mass movement 

 or/low) 

 Titter-conducting tissue of 

 , root, tracheae'* tracheids 



\ (?) 



Celts of root cortex 



T (osmosis) 

 ^ioot hairs - epidermis 

 I (osmosis - 

 imbibition)- 



Soil water 



Diagram of the path of water through a plant. The most important process 

 involved in each step is indicated. 



from the epidermis inward to the water-conducting tissue. Con- 

 sequently water may pass by osmosis from cell to cell across the 

 root to the tracheae. Mineral salts may diffuse across the cortex 

 into the tracheae. 



At this point the fourth factor in absorption enters. This is 

 the tension, or pull, on the water in the tracheae of the root caused 

 by the evaporation of water from the above-ground shoot. ^ 



^ Large trees have been kept alive for days by placing the cut-oflf trunks in water. 

 This shows that sufficient water to maintain the water balance of the plant for at 

 least several days may be lifted in a plant by the pull of transpiration without the 

 aid of roots. It is of practical interest to know that cut flowers will last much 

 longer if the ends of the stems are bent over into a vessel and cut under the water. 



