442 



PRIMA RF ARRANGEMENT OF TISSUES. 



Taxineac, the genera Saxcgothea, Dacrydiuni, Podocarpus (excepting the section Nageia), 

 and Tsuga with exception of T. Douglasii Carr. — there is one constant resin-passage 

 between the bundle and the epidermis of the lower surface of the leaf, either close to the 

 latter, often as a keel or ridge projecting outwards as in species of Juniperus, Thuja, and 

 Biota, or deeply embedded near to the bundle, as in Cunninghamia (Fig. 191). Besides 

 these there are in many species (e. g. Cryptomeria) accessory passages corresponding in 

 their arrangement to those which are constant in the Abietinese, One of these lies 

 (with the exception as above of Tsuga) at each lateral margin of the leaf close to the 

 upper surface; either this alone is present, e.g. always in Larix and Gedrus, or three 

 are also accessory ones in the hypoderma, the number and arrangement of which vary 



Fig. igi. — Cunninghamia sinensis ; transverse section through the leaf (220). 11 lower, o upper surface ; h resin 

 passage, xs hypodcrmal fibres, s sclerenchymatous fibres scattered in the parenchyma, g xylem of the median 

 bundle, ^ its border of tracheides. Below, and towards the resin passage, is the thin-walled phloem ; the white band 

 at its margin towards the parenchyma surrounding the resin passage is the compressed primordial tissue of the 

 phloem. 12 transversely-elongated parenchymatous cells of the middle of the leaf. 



according to both species and individual : e. g. in the needles of Pinus sylvestris to such 

 an extent that 1-22 of them have been observed. 



In the leaves of Sciadopitys 4-10 passages lie under the epidermis, which are dis- 

 tributed in varying symmetry over the margin and lower sides in relation to the simple 

 or double leaves. 



The leaves of Araucaria, Dammara, and Ginkgo, with several vascular bundles, are 

 traversed by at least as many passages as bundles ; they alternate with the latter in almost 

 the same plane. 



The passages in most cases pass continuously through the elongated leaves from the base 

 upwards, and end blindly at a distance from the apex, which varies sometimes with the 

 individual, sometimes with the species. Thus the median passage in species of Podocarpus, 

 stops far below the middle of the leaf. In the lamina of Ginkgo, in place of the 



