ANATOMY AND PHYLOGENY OF THE CONIFERALES. 



25 



of the first annua] ring of the root. The resin canals present under the conditions 

 described above are perfectly normal, and arc surrounded by a continuous picket of 

 resiniparons epithelium. A further mode of occurrence of resin canals in Abies is 

 that seen in the case of injury to the bast and cambium, either from mechanical causes, 

 or by the attack of parasitic fungi. The resin canals formed under these conditions are 

 generally confined to the wood, and occur as tangential rows of so called "imperfect 

 canals," which are in full communication with each other tangentially, and thus serve 

 to pour resin over the surface of the wound. The resiniparons epithelium in this 

 case is ordinarily thick walled and as a consequence conspicuously pitted. The 

 thickening of the wall seems to be merely a mechanical device, as all parenchyma of 

 the wood is more or less characterized by this feature in the vicinity of a wound. 

 Further, the resiniparons cells surrounding the traumatic resin ducts under consideration 

 are apt to partake of the general features of the parenchyma normally occurring in the 

 wood and the medullary rays. They may often as a consequence contain the globules 

 of tanniniferous material, which are so constant a characteristic of the so called resin cells 

 in Abies and other genera of the Abieteae as limited above. In the remaining genera, 

 Cedrus, Pseudolarix, and Tsuga, the normal occurrence of ligneous resin canals is confined 

 to the first annual ring of the root. Traumatic resin ducts are found in the last men- 

 tioned genera as a feature of the wood in the case of injury just as in Abies. It is of 

 importance to note, that in Cedrus, traumatic resin canals may occur both in the hori- 

 zontal and in the vertical planes, with correlation between the two systems. Only 

 vertical ducts have been made out in the other genera of the Abieteae. 



Before going on to discuss the significance of the structural features of the wood 

 summarized in the foregoing paragraph we may turn our attention to the distribution of 

 cortical resin canals in the Abieteae. In Abies and Cedrus, resin canals occur abundantly 

 in the cortex of both vegetative and reproductive axes and in the mesophyll of the leaf as 

 well. In Pseudolarix and Tsuga on the other hand, the resin canals of the cortex are 

 strictly confined to the female reproductive axis together with its appendages and to the 

 mesophyll of the leaves. Cortical resin ducts cannot be produced as the result of injury. 



The distribution of the resin canals in the wood and cortex of the Abieteae is such 

 that if the validity of the general principles enunciated above be admitted, we must 

 regard them as having come from ancestors having resin canals throughout their wood 

 and cortex, as is the case with the genera included in this memoir in the subfamily 

 Pineae. The resin canals in the Abieteae have almost entirely disappeared in the woody 

 tissues, only retaining their place in an isolated fashion in such conservative regions as the 

 wood of the 'female cone and the first annual ring of the root and shoot. They further 

 show their vestigial character in the phenomena of injury. In the cortical tissues there 



