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Table 1. Relationships of characteristics among the ‘original axis’ (above- and below-ground) of early vascular plants, and the shoots and roots of extant plants
Data from Bell (1991)
, Cutter (1971), Damus et al. (1997), Duckett et al. (1996), Eames (1936), Eames and MacDaniels (1947), Esau (1953), Fahn (1974), Gifford and Foster (1987), Goebel (1930), Groff and Kaplan (1988), Raven (1977, 1984a, 1986, 1993, 1995a, 1997), and Schneider (1996).
Characteristic
|
Shoot of extant plants
|
‘Original axis’ of early vascular plants
|
Root of extant plants
|
| Primary xylem |
Protostele in some pteridophytes; pith present in other vascular plants |
Protostele |
Non-medulated protostele (except some monocotyledons with central pith, i.e. medullated) |
|
pith present in other vascular plants |
|
(except some monocotyledons |
|
|
|
with central pith, i.e. medullated) |
| Root cap |
Absent |
Absent |
Present |
| Hairs |
Varied ‘shoot hairs’ usually present |
‘Axis hairs’; mycorrhizas |
‘Root hairs’; often supplemented by |
|
|
on below-ground parts |
mycorrhizas |
| Origin of branches |
Superficial origin of branch shoots. |
Superficial origin |
Endogenous origin of branch roots. |
|
Roots originating from shoots can |
|
Shoots originating from roots can |
|
be endogenous or exogenous |
|
be endogenous or exogenous |
| Endodermis in organs lacking |
Usually absent; present in many |
(Apparently) absent |
Present in almost all cases; |
| secondary thickening |
pteridophytes, some spermatophytes |
|
sometimes supplemented by |
|
|
|
an exodermis (endodermis-like |
|
|
|
hypodermis) |
|
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Table 2. Linear elongation rate of roots, root hairs, fungal hyphae and other structures as a function of the diameter of the organ and the medium (soil, air) in which elongations occurs
Determinants of the elongation rate of roots are discussed by Barlow (1973), Canny (1973), Lyndon (1973), Passioura and Ashford (1974), Cahn et al. (1989), Varney et al. (1991), Bret-Harte and Silk (1994), and Pritchard (1994). The very rapid elongation of aerial roots of Cissus can be related to the large number of enlarging cells in the 1 m long elongation zone. This long elongation zone is permitted in aerial structures where buckling, such as would occur in below-ground structures with a long elongation zone, is not a consideration.
Structure
|
Diameter
|
Extension rate
|
Reference
|
| Main root axis of small-grain cereal |
0.4–0.7 mm |
20 mm d-1 |
Scott (1977) |
| First order lateral root axis of small-grain cereal |
0.2 mm |
5 mm d-1 |
Scott (1977) |
| Second order lateral root axis of small-grain cereal |
0.05–0.1 mm |
1 mm d-1 |
Scott (1977) |
| Main root axis of the large-grain cereal Zea mays |
1 mm |
60 mm d-1 |
Scott (1977) |
| Root hairs |
10–15 µm |
2 mm d-1 |
Scott (1977); Sievers and Schnepf (1981) |
| Arbuscular mycorrhizal hyphae |
2–27 µm |
3 mm d-1 |
Smith and Read (1997) |
| Ectomycorrhizal hyphae |
2–3 µm |
2–4 mm d-1 |
Smith and Read (1997) |
| Free-hanging aerial roots of Cissus spp. |
1 mm over length of 8 m; elongation zone 1 m long |
240 mm d-1 |
Gill and Tomlinson (1975) |
| Underground stem (rhizome) of Pteridium |
3 mm |
3 mm d-1 |
Harper (1977); Page (1982) |
|
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Table 3. Cytoplasmic streaming speed in relation to the diameter of the spherical or cylindrical cells in which it occurs; temperature 20–25 °C
Organism, cell
|
Cell diameter (µm)
|
Streaming speed (µm s-1)
|
| Chara braunii cylindrical internodal axial or ‘leaf’ cells |
400 |
105 |
|
150 |
67 |
|
80 |
50 |
| Acetabularia calyculus cylindrical ‘shoot’ cell |
500 µm |
2.5-6.0 |
| Elodea canadensii spherical leaf cells |
30 µm |
3-10 |
| Higher plant root hairs |
10–15 µm |
4-10 |
|
References: Raven (1984c); Stebbins and Hyams (1979); Amos and Amos (1991); Table 2.
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