TS Bidens young stem

Anatomically the young Bidens pilosa is fairly typical of many herbaceous dicotyledonous stems. 

This young stem shown here is encased by a single layered epidermis, and underneath this are several layers of green-coloured cells, which are called chlorenchyma.  -This is photosynthetic tissue. It forms the outer cortex. The inner cortex is composed of 2-3 layers of parenchyma cells and directly underneath this is the starch sheath. The vascular bundles are associated with primary phloem fibres. Bundles contain proto (first-formed) and meta (last formed) xylem.

Par = parenchyma, SS = starch sheath, PPF = primary phloem fibres, PX = protoxylem, MX = metaxylem, Ch = chloroplasts, E = epidermis.

Click here to see electron micrographs of a chloroplast.