1920 J 



DUPLER— TAXUS CANADENSIS 513 



occurs in all known gymnosperms, excepting the Gnetales. In the 

 older forms it is more or less distinctly differentiated into the three 

 layers; in the modern forms one or more layers become "reduced," 

 as the outer fleshy layers in most conifers and the inner fleshy 

 layer in such forms as Taxus. On the other hand, the taxads are 

 pronounced in the retention of the outer fleshy layer, Cephalotaxus, 

 Torreya, and Taxus showing an excellent series both in the delay 

 in appearance and in the freedom from the stony layer, Taxus 

 showing both these features in greatest degree. 



Attempts have been made to relate the taxads to the cycads 

 on account of the fleshy character of the ovule, regarding Cephalo- 

 taxus and its relatives as bridging from cycads to conifers. The 

 cycadean origin of the conifers does not harmonize with the known 

 facts, however, and the attempt to relate all gymnosperms with 

 fleshy seeds in a common phylogeny is almost as absurd as to 

 attempt to construct a human " family tree" on the same basis. 

 The tendency to "fleshiness" is too scattered to have any phyloge- 

 netic significance in a broad sense, although it probably has value 

 within the narrower limits of small groups. 



Vascular features 



The vascular supply of the secondary shoot of T. baccata has 

 been described by Van Tieghem (37), Strasburger (35, 36), 

 and Miss Aase (1) . Van Tieghem was the first to apply anatomical 

 criteria to the morphological nature of the ovule, and concluded 

 from the origin, orientation, and structure of the vascular supply 

 that the ovule is a lateral structure, representing the first and 

 only leaf of a branch of the third order arising in the axil of the 

 "sixth scale" of the secondary shoot. According to his descrip- 

 tion, after the fertile scale has received its vascular supply, two 

 bundles leave the axis, turn in such a way that the xylem is oriented 

 outward, and these two bundles then penetrate the ovule, where, 

 after forming a "small vascular cup," they give off, ordinarily two, 

 sometimes three, or even four or five, branches into the integument. 

 He also gave the bilateral symmetry of the ovule as one of 

 the reasons for regarding it as axillary, bilateral symmetry 

 being characteristic of leaf structures as contrasted with stem 



