





252 



DB. M. T. MASTEBS ON THE MORPHOLOGY, 











well-defined situations. Thus in all the species of Tsuga there is 

 one central resin-canal immediately beneath the central vascular 

 bundle, and a similar arrangement prevails in Torreya, Cephalo- 

 taxus, Podocarpus, Saxe- Gothea, Sciadopitys, Fitzroya, Cryptomeria, 

 Sequoia, Taxodium, Juniperus, &c. 



In the species of Larix there are two canals, one at each angle 

 of the leaf beneath the epiderm. A very common arrangement is 

 that in which the canals are placed within the epiderm on the 

 lower surface on either side of the midrib, or there may be several 

 canals arranged all round the leaf at intervals beneath the epi- 

 dermis, as, for instance, in Pinus Strobus, monophylla, Cembra, 



* 



and in some species of Araucaria and Altingia. 



In other instances, as in Pinus Pinaster, mitis, inops, Tada, 

 Lambertiana, Araucaria imbricata, Abies Veitchii, Ac., &c., the 

 resin-canals are in the centre of the mesophyll, while in Pinus 

 pseudostrobus &c. they are almost or quite in contact with the 

 endoderm. In three-sided leaves of some species of Pinus, if 

 there be but one canal, it is placed under the epidermis in the 

 centre of one side, if three then there is one in each of the three 

 angles of the leaf. Engelmann accordingly spoke of the ducts 

 as peripheral, or subepidermal, parenchymatous, and internal, 

 and grouped the species of Pinus in large measure according to 

 the position of the ducts. 



The arrangement of the canals is sometimes different in the 

 primordial and in the secondary leaves respectively, and in Pinus 

 Lambertiana the resin-canals are sometimes subepidermal, some- 

 times parenchymatous. 



The canals are sometimes separated from the mesophyll by a 

 well-marked ring of thick-walled cells, often continuous with the 

 hypodermal cells, but occurring sometimes around those ducts 

 which are placed in the centre of the mesophyll ; thus the resin- 

 canals of Pinus are : 



1. Entirely surrounded by " strengthening-cells," e. g. Pinus 

 silve&tris, Laricio, Pinea, serotina, nigncans, Peuke, deflexa, pon- 

 der osa. 



2. Encompassed by thick-walled cells with thin-walled cells 

 intermingled, e. g. Pinus densiflora, Coulteri, Torreyana. 



3. Begirt by thin-walled cells only, e. g. Pinus maritima y hud- 

 sonica, Strobus,pyrenaica, ins ignis, Jeffreyi, longifolia, canariensis, 

 excelsa, argentea, monticola *. 



• 



# See Mobius, in Jahrb. f. wissenech. Botanik, t. xvii. p. 263 (1885) 







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