ANATOMY" AND IMI Y UHiKN Y OF THE CONIFERALES. 



J 9 



traumatic wood. Under these circumstances tangential rows of resin canals arc 

 formed in the spring wood of successive hut generally not consecutive annual rings. 

 Although a good deal of material has been examined from various sources and of 

 wide geographical distribution, no examples of horizontal resin canals have been found 

 such as are present in (Jedrus, described above. The resiniparous cells lining the 

 interior of the traumatic resin ducts in Tsuga are thick walled and much pitted. 

 They frequently contain dark brown tauniniferous globules or masses, similar to 

 those found in the resin cells of the normal wood of Tsuga. Traumatic resin canals 

 of a similar nature have also been found in Tsuga mertensiana. In this species they 

 are entirely confined to the aestival wood. It is thus possible to distinguish the two 

 species by the reaction of their wood to injury. 



In figure 49, plate 7, appears a transverse section of a yearling stem of Tsuga 

 canadensis. Although the branch is a vigorous one there is no evidence of the presence 

 of resin ducts. Even in the most flourishing branches of T. canadensis, bearing female 

 cones, there are no resin canals present in the first year's growth, such as are 

 found in similar shoots of Abies magnifica. Another feature of Tsuga shown in the 

 figure is the entire absence of cortical resin canals. This condition is likewise present 

 in T. mertensiana, which resembles T. canadensis in the structure of its woody tissues. 

 The cortex of the two species mentioned is also free from the mucilage cells which 

 are such a striking feature of this tissue in Abies and Pseudolarix. 



In figure 50, plate 7, is shown part of a transverse section of the cone of Tsuga 

 mertensiana. Although there are still no resin ducts in the wood of the large 

 cone of this species, they are obviously present in the cortex. On the right of 

 the figure two very large ducts are about to pass off into the fructiferous scale. Figure 

 51, plate 7, shows a similar view of a transverse section of the cone axis of T. 

 canadensis. In this case, too, cortical resin canals are present although there are no 

 ligneous ones. On the right and left of the figure, ducts are to be seen passing 

 out into the two fructiferous scales which are included in the plane of section. 

 It will be seen that Tsuga resembles Pseudolarix in the distribution of cortical 

 resin canals in the vegetative and female reproductive axis, for as in the latter 

 genus, they are present in the reproductive axis and in the fructiferous scales, 

 but are entirely absent from the cortex of the vegetative stem. As is well known, 

 there is a single median resin canal present in the mesophyll of the vegetative leaf 

 of Tsuga. 



In figure 52, plate 7, is represented a transverse section of the root of Tsuga 

 mertensiana. The magnification is just sufficient to show the presence of a median 

 resin duct in the primary wood. There are no resin canals present either in the 



