SYSTEMS OF TISSUE. 175 
While, namely, the cells of the developing tissue have not yet 
assumed a definite, permanent form, but become altered by di- 
vision and mutual dislocation, the cells of the permanent tissue 
are conclusively defined with regard to their form, or are sub- 
sequently but little changed. By far the most drugs consist of 
permanent tissue. 
In the angiosperms there are to be distinguished at the grow- 
ing point three meristem zones: the dermatogen’ trom which is 
formed the epidermis; the periblem,* from which is produced 
the bark; and the plerom,* from which are formed the vascular 
bundles and the medulla. In angiospermous roots there is, in 
addition, the calyptrogen,* deca represents the developing tis- 
sue of the root-cap. 
IV. Systems of Tissue. 
If, in grouping the forms of tissue as systems of tissue, the 
latter are viewed not alone froma purely anatomico-topographi- 
cal standpoint, but if, at the same time the question arises, im 
which manner the various tissues are of equal value physio- 
logically, they may be divided in the following manner: 
1. The epidermal system. Function: the protection of the 
organs from without. ) 
2. The mechanical system. Function: to give stability to the 
plant. 
3. The assimilating system. Function: assimilation of the 
carbon. 
4. The conducting system. Function: conduction, especially 
the conduction of water and nutritive salts from the soil, and to 
conduct away the products of assimilation. 
5. The storing system. Function: the storage of reserve nu- 
tritive substances and of water. 
6. The aérating system. Function: the aération of the or- 
gans. 
1 Aépua skin, and yervaéoI produce. 
2 TTep¢ around, PAyua covering. 
8 TAnp@ ya that which fills. 
4 Kalvarpa a cap. 
