ABSORPTION TISSUES 115 



sues of other plants, are usually lacking in root hairs. 

 Absorption of water in this type of plants may take 

 place through the modified epidermis of the aerial 

 roots which are usually present. For their supplies 

 of water, desert plants must depend largely upon 

 dew and very short periods of rain, as the soil in 

 which they live is almost devoid of moisture. Plants 

 living under these conditions have little need for root 

 hairs and these structures are usually lacking. The 

 leaf and stem epidermis of desert plants is so modi- 

 fied that absorption of water can take place through 

 these parts. As the roots of aquatic plants are sur- 

 rounded by water there is little necessity for an exten- 

 sive root hair development in these types. Root 

 hairs are very delicate structures and they are seldom 

 found intact in powdered drugs or foods. Where 

 plants are removed from the earth by force, the root- 

 lets bearing root hairs are usually detached and there- 

 fore are hot apparent, 



ABSORPTION OF GASES 



Absorption of gases takes place through small 

 openings termed stomata located in the leaf epidermis, 

 and through irregular fissures or lenticels occurring 

 in the periderm of mature plants. The gases entering 

 the plant through stomata or lenticels are distributed 

 to the individual cells by passage through intercellular 

 spaces or by gradual diffusion through thin-walled 

 cells. " -^ 



Stomata. — Stomata occur in the covering mem- 

 branes of leaves, herbaceous stems and sepals of the 

 flower (Plate 44). They are occasionally found in 

 the epidermal membranes covering the petals and 



