Stem Anatomy

The dimorphic branches of pepper exhibit minor variations in their anatomical features, though the basic structure remains the same in both. The orthotropic stem

Table 2.6 Spike (female) characters of Piper spp. closely related to pepper.

Species

Spike

Peduncle

Spike

Spike

Spike

Bract type

length

length

shape

orientation

texture

(mm)

(mm)

(Mean)

(Mean)

P. argyrophyllum

83.0

25.2

Filiform

Pendulous

Glabrous

Adnate

P. attenuatum

120.0

20.0

Filiform

Pendulous

Glabrous

Adnate

P. barberi

50.0

90.0

Cylindrical

Pendulous

Glabrous

Peltate, orbicular

P. bapnium

30.0

15.0

Cylindrical

Erect

Glabrous

Peltate, pedicelled

P. hymenophyllum

73.0

22.0

Filiform

Pendulous

Glabrous

Peltate, pedicelled

P. galeatum

105.0

17.4

Filiform

Pendulous

Glabrous

Connate, fleshy cup

P. longum

38.0

14.0

Cylindrical

Erect

Glabrous

Stalked, peltate, orbicular

P. mullesua

9.0

2.3

Globose

Erect

Glabrous

Stalked, peltate, orbicular

P. nigrum

105.0

10.7

Filiform

Pendulous

Glabrous

Shallow cup below the ovary

P. schmidtii

125.0

20.0

Filiform

Pendulous

Glabrous

Obconical, angular free margins

P. silentvalleyensis

40.0

1.3

Filiform

Erect

Glabrous

Stalked, peltate, orbicular

P. sugandhi

71.0

14.6

Filiform

Erect

Glabrous

Deeply cupular, stipitate

P. sugandhi var. brevipilis

69.0

14.0

Filiform

Pendulous

Hirtellous

Deeply cupular, stipitate

P. trieb ostacby on

76.0

15.3

Filiform

Pendulous

Hirtellous

Connate, fleshy cup

P. wightii

65.0

12.0

Filiform

Pendulous

Glabrous

Adnate with free margins

ffl O

TA N

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Ui Ui

Piper Argyrophyllum Anatomy
Figure 2.6 T.S. of leaf petiole showing the central mucilage canal (mu) and the vascular bundles.

(the monopodial main stem that climbs over support trees) exhibits faint longitudinal striations, resulting probably from the wavy band of vascular bundles and sclerenchyma. The anatomy of this stem is typical of that of Piperaceae and is the one studied most frequently (Metcalfe and Chalk 1950, Murty 1959, 1960, Pal 1961). The T.S. of the orthotropic stem reveals the following structure. The epidermis is made of rectangular cells over which there is a corrugated layer of cuticle. Below the epidermis there are 2-3 layers of collenchymatous hypodermis with many sclereids distributed in between the cells. A discontinuous band of sclerenchyma is seen inner to the collenchymatous hypodermis and this band consists of 4-6 rows. Just below the sclerenchyma band 2-3 layers of chlorenchymatous cells and 4-6 parenchymatous layers are present. The vascular bundles are scattered in pith region as in monocot stem and this according to Hutchinson (1959) is an indication of the Ranalean ancestry. The innermost row of the cortex consists of smaller cells arranged compactly forming an endodermis. A pericycle is visible in certain regions. The endodermis exhibits casparian thickening.

The most distinguishing feature of the pepper stem anatomy is the distribution of vascular bundles (Fig. 2.7). There is an outer ring of vascular bundles (cortical or peripheral bundles) and an inner ring of regular bundles (central or medullary bundles). The outer ring consists of small and large bundles arranged often alternatingly, they are collateral and open, and consist of a sclerenchymatous cap at the phloem end, below which lies phloem, cambium and xylem. There are 35-40 such bundles, each covered by an indistinct bundle sheath. The xylem consists of vessels, tracheids and fibres. The cambium consists of 3-4 rows of narrow elongated cells. The phloem is

Piper Argyrophyllum Anatomy
Figure 2.7 T.S. of stem showing the outer ring of vascular bundles and larger inner ring (medullary) of bundles.

comprised of sieve tubes, companion cells and phloem parenchyma. Below the peripheral vascular ring, there is a wavy band of sclerenchyma consisting of 5-6 rows of cells. The parenchymatous pith lies inside the wavy sclerenchymatous band, and consists of closely arranged parenchyma cells. Inside this region the medullary bundles are arranged. There are 8-10 bundles, larger than the cortical bundles. Each bundle has sclerenchymatous cap on either end. These bundles are also collateral and open. The xylem consists of vessels, tracheids and fibers. The average vessel and tracheid ratio is 8:3. Vessels are with pitted thickening and simple perforation plates, whereas tracheids are of scalariform and annular thickening type. Vessel ends vary from transverse to oblique and tails are absent at both sides. The cambium is 3-4 layered. The phloem consists of sieve tubes, companion cells and phloem parenchyma. The pith is very small, and at the centre of the pith there is a mucilage canal which forms a continuous canal traversing the entire plant body. This mucilage canal is lined with secretory cells similar to the pearl gland trichomes (Fig. 2.8)

Figure 2.8 A mucilage canal (mu) showing the secretary cells lining the canal.

The primary anatomical structure of the plagiotropic shoot (lateral shoot) differs from the orthotropic shoot in the following features.

1. continuous band of sclerenchyma in the outer cortex, whereas in the orthotropic stem this band is discontinuous

2. there are no sclerenchymatous caps over the peripheral (cortical) vascular bundles

3. lesser number of peripheral bundles (18-24) as compared to orthotropic stem (30-40)

4. lesser number of central bundles (4-6) compared to 8-10 in the orthotropic stem

5. fewer number of xylem elements both in peripheral and central bundles than that in orthotropic stem.

Shoot apex

The shoot apex shows the dome shaped apical meristem, leaf initials and axillary bud initials. The central mucilage canal is seen a little below the apical portion. During the very early stage of development itself the pearl gland trichomes get differentiated and they are present in plenty, giving a corrugated appearance to the cut edges of the developing leaves (Fig. 2.9).

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Responses

  • phillipp
    What are mucilage canals on black pepper plant?
    4 years ago
  • Erno Savolainen
    What is stem layer black pepper?
    2 years ago

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