. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. Cellulose additions to the wall fill thecell cavity down to the spreading base, where the cavity enlargesand is lined with an unusually thick protoplastic layer. Thewall separating the hair from the body of the leaf has many pitsthrough which the imbibed water can pass into a water reservoirtissue beneath, whence it is distributed directly to the mesophyllcells. The entire leaf is so thoroughly waterproofed that only ILLUSTRATIVE STUDIES 99 the basal part of the hairs can be wett
. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. Cellulose additions to the wall fill thecell cavity down to the spreading base, where the cavity enlargesand is lined with an unusually thick protoplastic layer. Thewall separating the hair from the body of the leaf has many pitsthrough which the imbibed water can pass into a water reservoirtissue beneath, whence it is distributed directly to the mesophyllcells. The entire leaf is so thoroughly waterproofed that only ILLUSTRATIVE STUDIES 99 the basal part of the hairs can be wetted. Nevertheless whena wilted leaf is submerged in water it soon regains its turgidity. Practically the same device with modified details is repeated invarious other desert plants whose roots donot go deep enough to draw water from thedepths of the soil. Although there are many devices for ab-sorbing water and solutes under variousenvironments, in one respect they are allalike: they are outgrowths that increase theabsorbing surface manyfold and enable theplant to make effective demands on thesource of 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 cavitynearly to base of hair;• b, water-storage cellscommunicating b ymeans of pits with thecell-lumen of the hair.(After Haberlandt.) Soak a flower pot in wrater. Soak mustardseeds in water overnight. Dash these seedsagainst the inner surface of the moist potwhere they will stick because of theirmucilaginous surface. Invert the pot in a saucer of water and theseeds will germinate and furnish an abundance of root hairs. Cutoff the roots and lay them in a dish of 5 per cent. KOH overnightto bleach and clear them up. Mount one of the cleared roots ina drop of the KOH solution under a coverglass and crush theroot a little by gentle pressure on the coverglass. Study withlow and high powers. Can you now make out that a root hairis
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