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Volume 63, 1934
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Key to the Microscopical Identification of Leaves of the Genus Pinus.

  • According to: Character of cross section.

    • Number and position of resin ducts.

    • Number and position of stomata.

    • Nature of hypodermal tissue.

A.

Cross Section—Triangular.

I.—

Resin ducts in twos:

Resin ducts median, stomata on all faces, in pairs P. Montezumae
" " " " fours P. leiophylla
" peripheral " " pairs P. Lambertiana
" " " " fours P. flexilis
" " " two faces only, in pairs P. strobus
" " " two faces only, over four (5 + 5) P. excelsa

II.—

Resin ducts in threes:

Resin ducts median, stomata on all faces P. Torreyana
" " and peripheral, stomata on two faces only P. Armandi

B.

Cross Section—Sector.

I.—

Resin ducts in twos:

Resin ducts median, stomata on all faces, number 15 + 9 + 9 P. taeda
" " " stomata on all faces, number 6 + 3 + 3 P. Sabiniana
" " " stomata on all faces, number 12 + 5 + 5 P. Coulteri (N.I.)
" " " stomata on all faces, number 9 + 5 + 5 P. radiata
" " " internal number 10 + 4 + 4 P. palustris
" " peripheral, stomata on all faces, number 3 + 3 + 3 P. canariensis
" " peripheral, stomata on two faces only, number 3 + 3 P. aristata

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II.—

Resin ducts in threes or fours:

Resin ducts median, with 1 water layer of hypoderm, 4 ducts P. scopulorum
" " " with 1 pseudo-water layer of hypoderm, 2–3 ducts P. rigida " " " with no water layer, but 3–5 rows of sclerenchyma P. ponderosa
" " " with no water layer, but 1 row of sclerenchyma P. Jeffreyii
Resin ducts internal with 1 hypodermal water layer P. caribaea
" " median and internal, with hypodermal water layer P. patula

III.—

Resin ducts five or more:

Resin ducts median, stomata on all faces, number 19-7-7, no water layer P. Coulteri (S.I.)
" " " of internal, stomata on all faces, number 8-5-5, 1 water layer P. tuberculata
" " " and peripheral, stomata on all faces, number 10 + 3 + 3, pseudo water layer P. yunnanensis

C.

Cross Section—Semi-circular.

I.—

Resin ducts absent, stomata 7–11, 1 water layer P. Murrayana
" " " " 6–9, 1 pseudo-water layer P. pinea

II.—

Resin ducts two to four:

Resin ducts median, 2, stomata 11 + 15, 1 water layer P. echinata
" " " 2, stomata 9 + 6, 1 or 2 sclerozed hypodermal layers P. luchuensis
" " " 2, stomata under 9 + 6, 2 hypodermal layers P. Banksiana
" " " "(and internal), stomata under 15 + 11 P. caribaea
" " " "3, stomata 12 + 8, two hypodermal layers P. Thunbergii
" " " "3, stomata 11 + 8, 1 water layer, stomata deeply sunken P. muricata
" " peripheral 2 and median, stomata 7 + 10 P. resinosa

III.—

Resin ducts five and over.

Resin ducts median, 9, stomata 15 + 8 P. pinaster
" " " 8–10, stomata 10 + 9 P. laricio
" " " 14, stomata 14 + 6 P. austriaca
" " peripheral, 6, stomata 6 + 3, two rows of sclerenchyma on are, 1 on base, only 2 resin ducts on upper face P. halepensis
" " " 6–8, stomata 8–8, 1 row of sclerenchyma on all faces P. Massoniana
" " " 7–9, stomata 10–7, no sclerenchyma, but a water layer P. densiflora
" " " 8, stomata 9–9, 1 layer of sclerenchyma, and 1 water layer P. sylvestris

D.

Section 4-sided.

Resin ducts peripheral, 3, stomata 4 + 4 on 2 faces only P. monticola

E.

Section Circular

Resin ducts, 2. peripheral P. monophylla