FORMS OF CELLS. 
51 
tively thin and consist chiefly of cellulose. The tissue 
consists either of single cells of indefinite length, as in 
the Asclepiadacese, or it may consist of a more or less 
branching net-work formed by the anastomosing of a 
number of cells, as in Taraxacum. It is distributed 
or associated with the sieve in nearly all parts of the 
plant; in the earlier stages the cells contain organized 
cell-contents which later disappear or are with difficulty 
distinguished from the other substances already enu- 
merated as present in the milk-juice. 
SECRETION CELLS OR RESERVOIRS. 
In Sanguinaria there occurs a rudimentary laticifer- 
ous tissue, most of the juice being contained, however, 
in special parenchymatous cells, which may be more or 
less isolated or arranged in irregular longitudinal rows. 
Cells of this character are known as secretion cells and 
usually contain oil, resin, tannin, calcium oxalate, mu- 
cilage, etc., instead of substances forming an emulsion 
or milk-juice; these cells are distributed in all parts of 
the plant, including the epidermal cells of secretion 
hairs. The walls usually consist of cellulose but may 
have lamellae of cutin and suberin, the latter being 
found particularly in the oil-secretion cells of rhizomes, 
roots, barks and fruits. 
In some instances mucilage cells containing raphides 
occur in longitudinal rows resembling the secretion 
cells of Sanguinaria ; in some of the ferns, the barks of 
elder and locust, and leaves of the Crassulacese, the 
tannin-cells are very much elongated, resembling the 
simple laticiferous cells in the Asclepiadacese. 
Oils, resin, mucilage, gum-resins and allied pro- 
ducts occur quite frequently in special reservoirs or 
cavities formed as already described in the footnote on 
page 33. 
