1920J DUPLER—TAXUS CANADENSIS 



499 



into two large bundles, which pass into the axis of the secondary 

 shoot (figs. 19-22), only a very weak vascular supply passing into 



primary 



condary 



each receives a pair of vascular bundles (figs. 23-27). Should 

 the primary axis grow out into a leafy shoot the next season, a 

 normal vascular cylinder develops, and the vascular supply to the 

 secondary shoot has the usual features of an axillary structure 

 (figs. 28-30). The normal continuation of the primary shoot in 

 its dwarf character during the next season results in a vascular 

 supply to the new growth, similar to that of the preceding season. 

 The vascular tissue of the new growth develops in connection with 

 the bases of the bundles which passed to the secondary shoot of the 

 preceding season, so that a series of sections shows a continuous 



•ndary 



small scale traces and bv a wide 



secondary shoot scar, where the bundle supply to the secondary 

 had passed off from the main axis. This gap, however, doe 

 have the ordinary features of a branch gap, being really th 



ding 



secondary 



from it as in ordinary 



gaps (fig. 32; cf. figs. 13, 14). The previously arrested and rudi- 

 mentary condition of the axis tip accounts for this behavior. The 

 xylem portion of the cylinder is relatively narrow, growth being 

 slow and uniform. Shoots more than one year old do not usually 

 show any growth ring excepting in the region of the secondary 

 branches of the preceding seasons, where the limit between the 

 xylem of the first and second season's growth is very distinct. 

 The xylem is endarch in the cylinder, but in the scales centripetal 

 wood may appear, although the scale traces in general are quite 

 short, frequently ending in the base of the scale. 



Morphological nature. — The morphological nature of the 

 primary shoot has been the subject of some question. It seems 

 clear that in Taxus the primary shoot is to be regarded as a vegeta- 

 tive shoot of limited growth, persistent for an indefinite period, 

 producing secondary fruiting shoots season after season, as a dwarf 

 shoot functioning only in this way. It may become a vegetative 



