TRANSACTIONS OF SECTION K. 761 



positions between tlie bundles b 1, b 2, andj,i 3, 6 4 respectively; while b 2, b 4, 

 and b l,b 3 are separated by the plumular traces d 2 and d 1 respectively. 



Following the hypocotyl downwards, the relations between the bundles are 

 somewhat complicated, c 1 and e 2 occupy their position throughout, but there is 

 much anastomosing between the bundles of the series b and d. At the same time 

 the protoxylems oi b 2, b 4, and b 1, b 3 rotate towards d 2 and d 1 respectively. 

 This rotation is, however, vacillating, and the rearrangement arrived at may be 

 obliterated by the formation of a branch passing from b S to d 1, for example. 

 Finally, however, the branching stops, the strands d 1 and d 2 having combined 

 with one of the bundles situated on their flanks, and a definite rotation of the 

 protoxylems b 2, b 4, and b 1, b 3 takes place. The condition now obtaining is 

 that of a tetrach root ; this last movement, however, is too late, for almost imme- 

 diately the phloem and metaxylem oi b 2, b 4, and b 1, b 3 fuse together, enclosing 

 in their meshes the exarch protoxylem which was derived from these same bundles. 

 Thus the groups of tracheids c 1 and c 2, which have been gradually increasing in 

 number, form the protoxylem of the dlarch root. 



Mirabilis divaricata, Lowe, follows a similar course. 



AMARANXACEiB : 



Amarantkus hi/pockondrtacus, L. — Each cotyledon has a single bundle. Bifur- 

 cation of the phloem and the rotation of the xylem towards the exarch position 

 commences some way up the petiole. On the central region of the axis being 

 reached, the rotation of the xylem is seen to be complete, the metaxylem elements 

 speedily pass inwards and, at a lower level, the opposing masses of phloem fuse 

 together. A diarch root is thus formed. 



The same changes occur in A. caudatus, L. 



The transition- phenomena in all the following plants are essentially of the 

 same nature as in Amarantkus : — 



AlZOACEiE : 



Tetragonia expansa, Murr., Mesembryanthemum crystallinum, L. 



Caetophtllace^ : 



Corriyiola litoralis, L., Lychnis Viscaria, L., Polycarpon tetraphyllum, L., 

 Silene Otites, Sm., and Silene pendula, L. 



P0ETULACACB.a3 : 



Portulaca oleracea, L., C(dandnnia Menziesii, Torr. et Gray. 



Chenopodiace.^ : 



Atnplex Aastata, L., Chenopodium Bonus-Henricus, L., Spinachia oleraeia, L. 



3. The Phylogenetic Value of the Vascular Structure of Sj)ermophytic 

 Hypocotyls. By A. G. Tansley and E, N. Thomas. 



The subject of this communication has been under investigation for several 

 years past. Owing to the vastuess of its extent the territory is still very incom- 

 pletely explored, but enough data have been brought to light to warrant a 

 preliminary setting forth of some results. 



The success of Jefl^rey, Gwynne- Vaughan, Boodle, and others in elucidating the 

 phylogeny of the vascular system of Ferns by a study of its ontogeny naturally 

 suggests a parallel investigation among flowering plants ; but here we are met by 

 a different type of early ontogeny depending on the habit of intra -seminal embryo 

 formation, and involving the appearance of the hypocotyl, an organ whose nature 

 and origin are ,«till the subject of dispute. Whether we regard the hypocotyl as 

 the equivalent of the first portion of the stem of a Pteridophyte, or as a new organ 

 developed subsequently to the evolution of the seed-habit, we clearly have to face 



