54 GROUPS OF TISSUES, OR TISSUE SYSTEMS 



(e) Root hairs may be studied in cross- or longitudinal-sec- 

 tions of the young roots of seedlings that have been germinated 

 between damp cloth or paper, or in moist air. By adding a 

 rather strong sugar, or potassium nitrate solution the cyto- 

 plasm may be drawn away from the walls sufficiently (plas- 

 molyzed) to become visible. 



(/) The leaves of various grasses (e.g. Panicum capillare) 

 will show simple one-celled hairs. The petunia stem possesses 

 unbranched hairs, consisting of rows of cells. Many will be 

 found to terminate in glandular cells. Hairs of these same types 

 ma}^ be found on tobacco, various species of Silene and very 

 many other plants. 



(g) The stems and leaves of various crucifers (e.g. Erysi- 

 mum, Arabis, Bursa), show bifid hairs. Stellate and peltate 

 hairs are shown best on the leaves of species of Elaeagnus and 

 Shepherdia. 



(h) The hairs of the common mullein (Verbascuin thapsvs) 

 may be studied as examples of greatly branched hairs. 



(i) Cross-sections of the leaf or stem of nettle (Urtica and 

 related genera) will show the peculiar stinging hairs. Under 

 high power note the terminal knob which breaks off as the hair 

 penetrates the skin, thus permitting the distended base of the 

 turgid hair to contract and discharge the poisonous contents 

 into the skin. 



77. The Conducting System. In most of the lower 

 algae and in the fungi, the plant body consists of separate 

 branching filaments, which are in some cases woven 

 together into a more or less firm body. These filaments 

 are about alike, and are mostly not differentiated into 

 conducting and other filaments. In some of the more 

 massive algae, however, as in the larger kelps (Laminaria, 

 etc.), or rock weeds (Fucus, etc.), the internal cells 

 are much more elongated, and seem to conduct the 

 elaborated food stuffs from one part of the plant to the 

 other, true sieve tissue sometimes being present. A 

 system of water-conducting tissue is not evolved until 

 the Mosses are reached. Here the center of the stem is 

 occupied by elongated cells, that serve probably in part 



