ILLUSTRATIVE STUDIES 



99 



the basal part of the hairs can be wetted. Nevertheless when 

 a wilted leaf is submerged in water it soon regains its turgidity. 



Practically the same device with modified details is repeated in 

 various other desert plants whose roots do 

 not go deep enough to draw water from the 

 depths of the soil. 



Although there are many devices for ab- 

 sorbing water and solutes under various 

 environments, in one respect they are all 

 alike: they are outgrowths that increase the 

 absorbing surface manyfold and enable the 

 plant to make effective demands on the 

 source of supply. 



ILLUSTRATIVE STUDIES 



FIG. 48. Water-ab- 

 sorbing hair of Diplo- 

 taxis Harra. a, second- 

 ary cellulose thicken- 

 ing of the cell-wall, 

 filling the cell cavity 

 nearly to base of hair; 

 b, water-storage cells 

 communicating b y 

 means of pits with the 

 cell-lumen of the hair. 

 (After Haberlandt.) 



Soak a flower pot in w r ater. Soak mustard 

 seeds in water overnight. Dash these seeds 

 against the inner surface of the moist pot 

 where they will stick because of their 

 mucilaginous surface. Invert the pot in a saucer of water and the 

 seeds will germinate and furnish an abundance of root hairs. Cut 

 off the roots and lay them in a dish of 5 per cent. KOH overnight 

 to bleach and clear them up. Mount one of the cleared roots in 

 a drop of the KOH solution under a coverglass and crush the 

 root a little by gentle pressure on the coverglass. Study with 

 low and high powers. Can you now make out that a root hair 

 is an outgrowth of an epidermal cell? Measure the length 

 and breadth of a hair and the thickness of its walls. Note the 

 tracheal tubes near the center of the root. Draw an entire 

 root hair including the enlarged basal part. Study a cross 

 section of a root put up in the form of a double-stained perma- 

 nent mount as described in Chapter XV. Find the stumps of 

 root hairs. Note the number and character of the cells which 

 the water and solutes absorbed by the root hairs must traverse 

 in going to the tracheal tubes. Draw a segment of the cross 

 section to show all this. 



