ANATOMY AND PHYLOGEN"? <)K THE CONIFERALES. 



7 



the two last annual lings of the (igure, dense tangential rows of resin canals can he 

 clearly seen on either side of an injured part of the stem. Figure II, plate 2, shows 

 a portion of the traumatic wood on the left of figure 10 more highly magnified. In this 

 case it is easy to make out- that the resin canals are more or less strikingly in tangential 

 communication with each other, and that they occur in the spring wood of each of the 

 annual rings formed subsequently to the injury of the stem. The canals in question 

 pour out a large amount of resinous secretion over the surface of the injured wood, and 

 by their presence as a reaction to injury only afford a much more economical provision 

 for antisepsis than the numerous resin canals which occur throughout the wood of Pinus. 

 In the annual rings of the stem shown in figure 11, both in those containing resin canals 

 and in those without resin canals, may be seen certain minute dark dots. These are 

 especially noticeable, in spite of the low magnification, in the annual ring immediately pre- 

 ceding those which contain resin canals. These dots are the so called resin cells, which 

 are frequently characteristic of those Coniferous w r oods which do not contain resin canals 

 under normal conditions. The dark color which is a feature of the cells in question is 

 due to the presence of a tanniniferous substance. In figure 12, plate 2, is seen a part 

 of the woody tissue from the axis of a witches' broom of Abies bedsamea. It is clear 

 from this figure that resin canals of the tangentially crowded traumatic type are also 

 present as the result of the attack of the fungus producing the witches' broom. This 

 feature has been described by Anderson ('97) and other pathologists. It is to be further 

 noted that the place of occurrence of the rows of traumatic resin ducts is in general the 

 same in the species under consideration, viz., in the spring wood. 



In figure 13, plate 2, is seen part of a section of an injured stem of Abies magnified 

 Murr. The area of the figure is all contained within the breadth of a single annual ring, 

 yet there are four rows of traumatic resin canals. This is the largest number occurring 

 within a single annual ring of wood which has come under my notice. Generally in the 

 various species of Abies there is but a single row of such ducts in a year's growth. The 

 position of the row of traumatic resin canals is usually constant in the same species, and 

 they may lie either in the spring or summer wood or in an intermediate position. 



Figure 14, plate 2, brings out an interesting peculiarity in the structure of the wood 

 of Abies magnified. In this species the resin canals which are normally absent in the 

 wood of the vegetative axis are found to occur with great constancy in the woody axis of 

 the cone. I have already referred to a similar phenomenon in the first memoir of this 

 series devoted to the anatomy of Sequoia. In S. gigantect in all the numerous cones 

 which have come under my notice from various sources, resin canals have always 

 appeared in the axis of the female cone, although they are normally quite absent from 

 the annual rings of the older parts of the stem and branches. I have had access to four 



