398 Mr Potter, On the Monocotyledonous plant. [May 28, 



the tigelluni. When the Cotyledons of the seedling are opposite, the 

 collateral bundles divide and descend through the hypocotyledonary 

 portion of the stem to the root, the Xylem separating from the 

 Phloem. The Phloem bundles now unite in pairs, each bundle uniting 

 with its neighbour and forming the Phloem bundles of the root : 

 the Xylem bundles rotate, so that the protoxylem becomes the most 

 external part of each Xylem bundle and the secondary Xylem the 

 most internal, and then uniting in pairs each one with the nearest, 

 the protoxylem uniting with protoxylem, and the secondary Xylem 

 with secondary Xylem. The Xylem bundles so formed coalesce 

 with each other to constitute the central Xylem of the root. 



In the case above described the number of Xylem and Phloem 

 bundles in the root is even, but in those cases in which the Coty- 

 ledons are not placed opposite each other, their divergence being 

 I or §, the number of Xylem or Phloem bundles is odd, being 

 3 or 5 respectively. The odd bundle situated on the opposite side 

 of the stem to the Cotyledons does not come from the Cotyledons 

 but from the lowest leaf of the stem. The bundles from the Coty- 

 ledons continue in the manner described above, the odd bundle 

 coalescing with the others to form the axial fibrovascular cylinder. 



In the Monocotyledon the root arrangement of the bundles 

 continues nearly as far as the point of insertion of the Cotyledon 

 in Phoenix Dactylifera or of the scutellum in Zea Mais. At 

 this point in Phoenix Dactylifera each Xylem and Phloem bundle 

 gives off a radial branch to the Cotyledon, and above this 

 the Xylem and Phloem bundles unite in pairs to form collateral 

 bundles. In the root each Xylem bundle has the protoxylem at 

 its exterior. The number of constituents of this protoxylem in- 

 creases before the branch is given off to the Cotyledon, and 

 generally the rotation of each Xylem bundle begins after the 

 bundle has branched, but in some cases it appears to have com- 

 menced before the branch is given off. This rotation is completed 

 before the Xylem and Phloem unite to form the collateral bundles 

 of the growing apex of the stem. In Zea Mais, at the insertion 

 of the scutellum there is a node where the bundles anastomose. 

 Here I have not been able to trace the course of each bundle. 

 The bundles depart from the regular type of the root just before 

 this node and the Xylem commences to rotate; above the node 

 we find the protoxylem the most internal part of a more or less 

 continuous ring of Xylem showing that the rotation is complete, 

 but that the pairing off of the Xylem and Phloem is not finished. 

 This arrangement continues as far as the next node, where again 

 there is an anastomosis, and above this we find the Xylem and 

 Phloem united in pairs to form collateral bundles. 





