TRACHEARY TISSUE 35 
those cells that happen to be so placed that a thickened angle 
appears in the section will show this feature. On the other 
hand, if the section passes between the corners of the cell the 
walls will appear thin. 
(g) Collenchyma may be found also in the young green shoots 
of elder (Sambucus) and some other shrubs, in the stems of 
lamb’s quarters (Chenopodium), pigweed (Amaranthus), 
petioles of beets and very many other plants. ; 
(hk) Make thin longitudinal sections of the wood and bark of 
the basswood (Tilia) or maple (Acer) and macerate, to 
separate the cells, in Schulze’s reagent (i.e. heat in a test tube in 
nitric acid to which has been added a little potassium chlorate). 
Mount a bit of the macerated wood section on a slide and tap 
the cover glass, or tease the section apart with needles. 
Study the wood fibers. Do the same for the bast fibers in the 
bark. 
(t) Now make thin longitudinal and cross-sections of the 
same kind of twig without macerating and study the fibers in 
place to note the relation of the overlapping cells. In the cross- 
section, note the appearance of the fibers and their position in 
the twig. 
45. Besides the foregoing, there is a group of tissues 
which have as their chief function the conduction of 
water and food, the so-called conductive tissues. ‘These 
are of three kinds: tracheary tissue, whose primary func- 
tion is the transportation of water, and sieve and lat- 
iciferous tissues, which are chiefly concerned with the 
conduction of food substances manufactured by the 
leaves. 
46. Tracheary tissue is of many kinds. Thetermishere 
used to include those elongated cells, whose chief function 
is the transport or storage of water. The lumen is usually 
rather large with the wall thickenedina more or less regu- 
lar manner to give strength. At the same time, a consider- 
able portion of the wall remains thin, permitting the en- 
trance or exit of water. The cells are not living, i.e. their 
protoplasm dies as soon as they have attained their final 
