







ANATOMY, AND LIFE-HISTORY OF THE CONIFEBiE. 



243 





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but the vaginal portion of the stalk is absent unless the 

 " pulvinus " be taken to represent it, a matter discussed under 

 the heading of the minute anatomy : suffice it here to say that no 

 such pulvinus occurs in these plants at the base of the perulae, 

 whose vaginal character will not be contested. 



In the Red-~Wood (Sequoia sernpervirens) , in Cunninghamia, in 

 Cephalotaxus, Torreya, Podocarpus, and others, the perul© are 

 also broad-based, sheath-like, and have no pulvinus. In some of 

 these plants, moreover) the base of the laminar or laminoid 

 portion is not contracted into any petiole, but is concrescent 

 with the stem (decurrent). 



In many Conifers the leaf, in the adult state, is represented 

 by the petiolar portions only ; but in other cases, as for instance 

 in the bracts of the cone of Eseudotsuga Douglasii, there are in- 

 dications of vaginal and petiolar portions. 



Arrangement of Leaves — Homotaxy and Heterotaxy. — The 

 phyllotaxis of the leaves of Conifers is treated of in various 

 text-books, so that a few peculiarities are all that demand atten- 

 tion in this place. Sometimes, as in Sequoia gigantea, Araucaria 

 imbricata, Abies Pinsapo, the foliage is arranged in the same way 

 throughout the entire tree (Jlomotaxy). More usually the 

 arrangement varies in different parts of the tree. A change in 

 the phyllotaxy is of course common in the case of the bud-scales, 

 and also in the passage from the primordial to the adult foliage : 



in young plants of Thuya gigantea the leaves may be seen 

 in two, three, or in four ranks. In other cases the change is 

 more apparent than real, being brought about by concrescence 

 m various degrees, the concrescence alternating more or less 

 regularly with dialysis or freedom. Again, on the erect " leader- 

 shoots " of various species of Abies, Picea, Pjeudotsuga, Tsuga, 

 Ta.vus, Cephalotaccus, &c, the leaves spread on all sides, while on 

 the lateral branches, which spread more or less horizontally, 

 fc hey are arranged nearly in one horizontal plane*. In such 

 cases the phyllotaxis is not altered, but the leaves are twisted 

 more or less at the base so as to make them apparently di- 

 stichous, while in reality they are still polystichous. Occasionally 

 some of the side shoots will suddenly quit the horizontal 

 direction and assume an erect attitude, as in Picea Menziesii 

 and P. ajanensis. When this happens, the leaves spread on all 



Abies Pinsapo forms a constant exception to this rule, the leaves being in- 

 ™«*ly spreading in all directions. 



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