. Fossil plants : for students of botany and geology . Paleobotany. 130 CONIFERALES (RECENT) [CH. great majority of Conifers which are normally without resin-canals in the wood have the power of producing them in response to traumatic stimuU. In Cedrus, Pseudolarix, and Tsuga resin- canals are usually confined to the primary xylem of the root but wounding induces the development of canals in other parts of the wood. In Cedrus, however, both horizontal and vertical trau- matic canals may occur whereas in other Abietineae the traumatic canals are only vertical^. Resin-canals may occur in the fir
. Fossil plants : for students of botany and geology . Paleobotany. 130 CONIFERALES (RECENT) [CH. great majority of Conifers which are normally without resin-canals in the wood have the power of producing them in response to traumatic stimuU. In Cedrus, Pseudolarix, and Tsuga resin- canals are usually confined to the primary xylem of the root but wounding induces the development of canals in other parts of the wood. In Cedrus, however, both horizontal and vertical trau- matic canals may occur whereas in other Abietineae the traumatic canals are only vertical^. Resin-canals may occur in the first-year wood of some species of Abies (fig. 690, B) and in Sequoia gigantea they are present in the first-year wood of vigorous branches and in the peduncles of cones, but do not normally occur in the later wood. In S. sempervirens canals are as a rule absent and are developed only after wounding (fig. 690, A). In the Araucarineae. A B Fig. 690. A, Sequoia sempervirens. B, Abies sp. shomng traumatic canals in the wood. (After Jeffrey.) resin-canals are absent nor are they produced in injured stems: this failure to produce canals in response to disturbances set up by wounds is considered by Jeffrey to be an indication of the relatively late evolution of the family. Pinus, with abundant canals, is regarded as one of the more primitive types; Abies, with very few canals in healthy specimens but readily producing them on wounding (fig. 690, B), is regarded as a slightly later product of evolution, while Sequoia semfervirens (fig. 690, A) in which traumatic canals alone occur is still further removed from the original stock, and the Araucarineae, which are considered to 1 Jeffrey (05) p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Seward, A. C. (Albert Charles), 1863-1941. Cambridge : University Press
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