Most plants have ___________ to support ____________ which weigh many times their own mass. Although stems must be strong to hold __________ in the _______________, they also must be _____________ enough to bend in the wind. At the same time, stems must transport ___________ and _______________ almost continuously.
Stems are usually ______________ and _________________ in shape. Leaves are attached to the stem at the __________. The portion of the stem between the _________ is called the ________________. Plants which grow in open, unshaded places often have __________ _______________ (eg. _________________). In most plants, the internodes are _________ and the _____________ are held apart (see Fig. 12.10).
Stems grow in length because they have special regions at their tips called ______________. All the tissues produced by the stem tip are called _____________ tissues. Plants that live for a short time have ________, non_________ stems that consist only of ______________ tissue. Plants that live for longer periods of time usually have ________ ___________ stems. The woody tissues are produced by ________________ meristems which cause the plant to grow in ______________. All woody tissues produced by ________________ meristems are called ________________ tissues (see Fig. 12.11).
Some stems are modified for a special ________________. In grape vines, _____________ branches develop as _____________ which twine around other plants for _____________. Another specialized stem is the ___________. These are underground stems that are modified for ______________. The edible ______________ is an example of a tuber. Tissues in the tuber stem swell and become filled with _____________ (see Fig. 12.12 and 12.13).
A single layer of __________________ cells, covered with a _____________, protects the stem surface. Inside the stem, long strands of _____________ tissues called _______________ bundles connect each leaf with the ___________. Each vascular bundle consists of both ___________ and _____________. In the stems of __________, the vascular bundles appear to be arranged in a __________. In contrast, the vascular bundles in a monocot stem appear to be _________________ (see Fig. 12.14).
The tissue between the ________________ and the _______________ bundles is called the ___________. The cortex may consist of ____________________ parenchyma cells or ________________ parenchyma cells or even strengthening ____________________ cells. The tissue to the inside of the vascular bundles is called ____________ (see Fig. 12.14).
At the beginning of growth, the stems of ______________ shrubs and large trees have only _____________ tissues. As the stems become larger, the _________________ meristem (called the vascular _______________) is formed. This is a sheet of cells that divides rapidly and produces secondary _________ and secondary _____________. Over time, the secondary xylem cells form the _________ and the secondary phloem cells form the living part of the __________ (see Fig. 12.15).
Wood is made up of ____________ types of cells: (i) _____________ members form the long hollow pipes that conduct ____________ and dissolved ________________, (ii) ____________________ cells store _________________ and produce substances that prevent ___________ growth, (iii) _________________ fibres make up most of the wood and provide ________________ strength for support (see Fig. 12.16). Annual ______________ rings in the wood are created due to the difference in the growth of each cell type during different seasons (see Fig. 12.17).
Examine Fig. 12.18. Each year, the vascular _______________ produces more cells on the outer side of the stem. These become the bark which consists of ________ (outermost), non-functional _________________ phloem (middle), and _________________ secondary phloem. The outer layer (________) is a protective tissue, impervious to the movement of _________ and gases. To allow gases to diffuse in and out, specialized regions in the cork have air spaces called _____________ (see Fig. 12.19).