1909] ' DORETY—MICROCYCAS CALOCOMA 141 



approximation. In these situations, the xylem of one strand faces 



that of the other, giving to the inner one an inverse orientation 



(d, figs. 1, 2). When the fusion of two bundles is complete, the 



combination presents the appearance of a single concentric 

 strand. 



All the cotyledonary traces are derived from the branching of 

 three, which join the central cylinder (fig. j) in a manner similar to 

 that described by Matte (ii) and Thiessen (12) for Dioon edule, 

 and by the present writer (7) for Ceratozamia. The wood remains 

 endarch as far out as the sheathing "base of the cotyledons (fig. 13); 

 it becomes mesarch in this region ; and in the upper portion of the 

 blade the wood in the greater number of the strands is exarch. 

 Transfusion tissue is abundant, and in close connection with the cen- 

 tripetal xylem. Mucilage ducts alternate with the cotyledonary 

 traces. Tannin cells are conspicuous in the peripheral region. 



The hypocotyl has no vascular plate, no protostele; the passage 

 from stem to root is therefore easily studied. The four cotyledonary 

 strands remain distinct throughout this portion of the axis, only fusing 

 aterally with the few elements of the leaf traces still remaining to 

 «m a very imperfect siphonostele. Their elements finally unite 

 ^t those of the four root poles. The metaxylem and phloem 



nT C ' aS USUa1, and the resul ting portions swing to right and left, 

 of " " ght half of the phloem of each joining with the left half of that 

 phi C neXt ' WUh sometimes the lowermost extremities of leaf-trace 

 isticT mterVening &*• 4a). There is thus produced the character- 

 fan-srfT* StrUCtUre ' four g rou Ps of phloem alternating with four double- 

 often aPCd Xylem groups - Irre g ul ar proliferation of the medulla 

 (fig ^ Separates the Phloem group again into its two constituents 



Ve rv br I C ° rteX ° f the h >'P ocot y l were discovered the remains of a 

 tissue c° H Z ° ne ° f Cambium ' No traces, however, of any vascular 

 too exn h be deteCted outsid e the central system in seedlings with 



The r • leaVGS and SCVeral ° thers devel °P in g- 

 4 a ) ^ ™^ ln a11 the seedlings under observation was tetrarch (figs. 



toteOaged a redUCtion to'triarch toward the tip, in some cases. 

 into the 6 UCtS arC numerous in the hypocotyl, but do not penetrate 



ro °t- Neither pericycle nor endodermis is distinct in these 



the 



