Teak and pine are most suitable for the study of critical secondary growth because in secondary growth, secondary tissues are formed from lateral meristem which is well developed in these two cases and secondary growth occurs in gymnosperms and dicots.
In plants, conducting tissue xylem has an important integral cell as xylem vessel which is enucleate.
The phloem on other hand has a row of sieve tubes which are also enucleate at maturity.
Primary Meristems : They are those meristematic tissues which are dervied directly from the meristems of the embryo and retain their meristematic activity.
They are present at root, shoot tip and leaf primordia.
Root shows the following regions Root cap or calyptra - caplike protective covering over tip of the root Meristematic region is the subapical position Zone of elongation - receives new cells from the growing point Root hair zone - is the zone of differentiation Zone of mature cells - having thick walled impermeable cells.
The apical meristem of the root is present at all the root tips.
Apical meristem is subterminal in position of the growing root tips and responsible for terminal growth of the root in plants.
The major storage component of Avocado fruit is oil. It is stored in specialized mesocarp cells called idioblast.
In monocotyledons the seeds are generally endospermous.
The internal structure of grain can be studied in a longitudinal section.
It shows two distinct regions upper large region, the endosperm and lower smaller region, the embryo.
The endosperm is surrounded by a special one cell thick layer, called aleurone layer.
It is filled with aleurone grains which are proteinaceous in nature.
Other components of this layer are phytin, carbohydrates and small amounts of phospholipids are also present.
In most of the gymnosperms, like conifers and cycads, vessels are absent and the wood is made entirely of tracheids.
Such wood is known as nonporous.
In angiosperms, on the other hand, the wood consists of both tracheids and vessels.
The wide vessels appear as pores between otherwise small sized tracheary elements.
Such a wood is known as porous.
In porous wood, if vessels have essentially equal diameters and are uniformly distributed throughout the ring, the wood is known as diffuse porous.
It is characteristic of plants growing in tropics.
Chlorenchyma cells are those parenchymatous cell which contain chloroplast in them.
They are capable of photosynthesis.
A spore capsule of moss can perform photosynthesis, thus chlorenchyma are present in them.
The cells of queiscent centre have lower concentration of DNA, RNA and protein as compared to other cells in the root apex.
These cells do not divide, hence cytoplasm is light and nuclei are small in them.
This concept is based upon quiescent centre theory proposed by Clowes (1961).
