ANATOMY AND PHYLOG EN Y OF THE CONIFERALE8. 



L5 



lower border of the leaf. It will thus be seen thai resin duels are present in the cortical 

 tissues of the leaf in Pseudolarix, as well as in the female reproductive axis, although 

 they are quite absent from the cortex of the stem. From the fad thai there arc two 

 resin canals only present in the leaves (/. e., sterile bracts) of the female reproductive 

 axis, it may perhaps be inferred that two is the primitive number for Pseudolarix. It 

 should he stated at this point that the two resin canals of the sterile bracts end blindly 

 below, just as do those of the ordinary vegetative leaves, in spite of the fact that the axis 

 to which they are conjoined, unlike the vegetative, possesses cortical resin ducts. 



It will be seen from the foregoing paragraphs that resin ducts are present in the 

 wood of Pseudolarix under two conditions, viz., normally in the primary wood of the root 

 and as the result of injury in the secondary wood of both root and shoot. In the cortical 

 tissues they are normally present in the reproductive axis, the ovuliferous scales, the 

 sterile bracts, and the ordinary vegetative leaves. They do not occur in the vegetative 

 branches nor the root even in response to injury. 



It may be noted by looking a little closely at the fibrovascular bundle of the leaf of 

 Pseudolarix, reproduced in our figure 36, plate 5, that the leaf trace is double, being 

 divided into two by a parenchymatous strand passing through the xylem. As in the 

 genera already described, the leaf trace in the genus under consideration is very dis- 

 tinctly double in the outer cortex of the axis, although it departs from the central 

 cylinder as a single strand as in Picea. 



Cedrus. 



In the case of this genus we shall first examine Cedrus atlantica. The material 

 studied came from a small tree of the variety fjlauca growing in the Hunnewell pinetum, 

 at Wellesley. As is well known, those fossil woods which are without resin cells or resin 

 ducts, which do not possess spirally marked tracheids, and have their bordered pits 

 opposite and not alternating in the same tracheid, are united in the structural genus 

 Cedroxylon. The characters just enumerated are found in the wood of Cedrus atlantica. 

 Although resin canals are normally absent in the wood of this species, they occur 

 frequently as a result of injury under the same conditions as in the genera previously 

 described. Figure 37, plate 5, shows the structure of the wood on the margin of a wound 

 in the species being considered. Resin ducts of the usual type form a continuous row, to 

 the right of the area of injury. The cells surrounding the canals in this case are thick 

 walled and partially lignified as in the traumatic resin canals of some of the other genera 

 described above. They are enabled to pour out their secretion by the presence of numer- 

 ous pits. In figure 38, plate 5, is seen a transverse section of a w T ounded root of Cedrus 



