PLANT TISSUES 113 
Srmp.e Tissues are those which are composed of one kind of 
cell, as ordinary parenchyma, collenchyma and sclerenchyma, whereas 
CompLex Tissues are made up of two or more kinds of cells as 
xylem and phloem. 
The adult or permanent tissues represent those which have 
been laid down by the cell-division of meristems. 
Primary MEeErIsTeMs.—As was shown by Hanstein,' the 
embryo of Angiosperms, while still constituted of only a few 
cells in the process of division, becomes differentiated into three 
layers of cells which differ in their arrangement and direction 
of division; these were called by him Dermatogen, Periblem and 
Plerome. In roots a fourth layer of cells is sometimes evident 
at the apex. This was termed by Janczewski” the Calyptrogen 
layer. These primary layers or groups of cells are called 
primary meristems or generative tissues. ‘They are composed of 
more or less rounded cells having delicate cell walls of cellulose 
which enclose protoplasm and nucleus, and wherever found in 
living embryos are in a rapid state of division. 
The primary meristems or generative tissues are found in the 
growing apices of plant organs, such as root, stem and leaf 
apex. By the division and redivisions of their cells they give 
rise to the mature or adult tissues of plants. 
1. DeERMATOGEN or PROTODERM Originates epidermal tissue 
and derivative structures such as stomata, non-glandular and 
glandular hairs, glands, and sometimes cork cambium. 
2. PeRIBLEM or GROUND MERISTEM originates primary cortex 
tissue, chlorophylloid cells (chlorenchyma), colloid cells (collen- 
chyma), strengthening cells (sclerenchyma), crystal cells (raphi- 
derchyma), latex cells (lacterchyma), pericycle, endodermis, 
sometimes cork cambium and pith. 
3. PLEROME or PRocamsriuM originates the primary or first 
fibrovascular bundles, the cambium and sometimes the pith. 
According to the structure of the component cells and their 
location, the following tissues are found in various forms of higher 
plants: 
. Hanstein, “Die Scheitelzellgruppe im Vegetationspunkt der Phanerogamen,” 
Bonn, 1868. 
2 Am. Sci. Nat. 5 série, tom. xx. 
