CONIFERALES (PINACEAE) 231 



strands in each cotyledon (141). The solitary strand in each cotyle- 

 don of such polycotyledonous forms as Chauveaud observed, how- 

 ever, may hold some relation to the number of cotyledons (p. 297), 

 and so may not contradict the primitive character of the double trace. 



A study of the vascular anatomy of seedlings of Pinaceae has 

 developed some interesting facts. It will be remembered that the 

 so-called cycadean type of seedling consists of three or four vascular 

 bundles at the base of each cotyledon, which are connected with 

 three poles of a tetrarch root that generally becomes diarch below 

 (120), a type of seedling that characterizes both Cycadales and 

 Ginkgoales. Among Pinaceae, however, the cotyledonary strands 

 (one for each cotyledon) are connected with the poles of a diarch root, 

 excepting the Araucarineae, which have seedlings of the general 

 cycadean type. On the basis of this character, therefore, the cycads. 

 Ginkgo, and the araucarians are in the same general category (with 

 numerous cotyledonary strands). The difference between the cycads 

 and Ginkgo on the one hand and the araucarians on the other should 

 be noted. While in the former groups the cotyledonary strands are 

 definitely three, among the araucarians they are usually four to eight 

 (154) ; while in A. BidwilUi they are twelve to sixteen (161). In this 

 last form the protoxylem poles of the root are also quite variable in 

 number (5-7), and their connection with the cotyledonary strands 

 is complex and variable. This pentarch to heptarch root becomes 

 reduced finally to the diarch condition. The contrast of the cycads^ 

 Ginkgo, and the araucarians with the other Pinaceae, therefore, is 

 that in the latter the cotyledonary strands are single and the primary 

 structure of the root is diarch, while in the former groups the cotyle- 

 donary strands are three or more and the primary structure of the' 

 root is tetrarch or some higher order, but eventually becomes diarch. 

 The most obvious contrast is with the Cupressineae and certain 

 Taxodineae, which have two cotyledons, each with a single vascular 

 bundle at base; among the other Pinaceae the situation is complicated 

 by polycotyledony (135). 



In this connection attention may be called to the fact that in tracing 

 the vascular bundles from the transition region of the seedling (the 

 cotyledonary node) to the root, they become exarch. This persistent 

 exarch character of the primary xylem of all roots was long ago 



