GYMSOSPERM^S. 409 



bium at the time of activity in the cambium of tlie fibro- 

 yascular bundles, there is an annual addition made to the 

 fundamental tissues of the stem corresponding to the addi- 

 tion made in the fibro-vasciilar bundles. 



519. — By this internal increase of tissues in the stem the 

 epidermis is at length ruptured, and the primary cortex be- 

 comes exposed, and eventually broken up and destroyed. 

 The phloem portions of the fibro-vascular bundles, and the 

 subsequent external additions to the fundamental tissues 

 made by the inter-fascicular cambium, constitute what is 

 called the Barh of the stem. There are usually in it corky 

 developments, which often very considerably change the 

 character and alter the relations of its parts. The paren- 

 chyma frequently becomes somewhat sclerenchymatous, while 

 in other cases it undergoes a peculiar degeneration. 



520. — Most Gymnosperms have intercellular canals in 

 their stems, either in the flbro-vascular or the fundamental 

 portions ; these contain a turpentine in which is dissolved a 

 resin.* 



521. — There are three quite well-marked orders of Gym- 

 nosperms, which may be separated as follows : 



1. Cycadese, the Cycads. Stem simiole, or rarely branched, 

 not resinous ; pith large ; leaves largo, pinnately compound, 

 crowded upon the stem. 



2. Coniferae, the Conifers. Stem branched, usually resin- 



* Tlie distribution of tliese canals has been made out by Van Tieghem 

 {Ann. des Sci. Nat., 1872) to be as follows for the principal genera of 

 Goniferaa : 



1. No canals in root or stem — Taxus. 



2. Canals in the stem only. 



(a) In the cortical parenchyma — Taxodium, Podoearpxis, Tor- 



Tcya, Tsuga, etc. 

 (J) In the pith also — Ginkgo. 



3. Canals in both stem and root. 



In the cortical parenchyma of the stem — Cedrus, Abies, etc. 



(a) In the xylem of the fibro-vascular bundles of root and 



stem — Pinus, Larix, Picea, Pseudolarix. 

 (6) In the phloem of the fibro-vascular bundles of root and 



stem — Thuya, Ciiprcssus, Bv4a, Araucaria, etc. 



