Seedling Structure of Gymnosperms. IV. 
33i 
Transition. 
9. The transition to root-structure takes place in the lower region 
of the hypocotyl ; in Welwitschia and Gnetum at the level of and 
immediately below the foot. 
10. Each pole of the root-structure is formed from two cotyledonary 
bundles which rotate towards each other and outwards, and so bring their 
protoxylems into an exarch position. These groups of elements become 
more compact, and the corresponding metaxylem-masses come into con¬ 
tinuity. The groups of phloem elements pass towards the intercotyledonary 
plane, but their fusion may be delayed considerably. 
11. In all cases the primary root is diarch. 
12. In Gnetum the primary root remains short and peg-like for some 
time; later, it elongates after two or three lateral roots have been formed. 
In Ephedra and Welwitschia there is no delay in the growth of the primary 
root. 
EXPLANATION OF FIGURES IN PLATES XXII AND XXIII. 
Illustrating Mr. T. G. Hill’s and Miss de Fraine’s paper on the Seedling 
Structure of Gymnosperms. 
Abbreviations used region of insertion of foot: L.S., longitudinal section: mx., metaxylem: 
ph ., phloem : px., protoxylem : s,, foot; T.S. transverse section. 
PLATE XXII. 
Figs. 1-5 x 240. 
Fig. 1. Ephedra distachia. T.S. of part of cotyledon. 
Fig. 2. E.fragilis. T.S. hypocotyl, showing the transfusion tracheides. 
Fig. 3. E.fragilis. The same in L.S. 
Fig. 4. Welwitschia mirabilis. T.S. of part of cotyledon. 
Fig- 5. If 7 , mirabilis. T.S. hypocotyl, showing a vascular bundle and isolated protoxylem 
elements. 
PLATE XXIII. 
Figs. 6-20 natural size. 
Fig. 6. Ephedra distachia. Young seedling. 
P’ig. 7. E.fragilis. Older seedling. 
Fig. 8. E. campylopodia. Still older seedling, showing the much elongated seed-leaves and the 
plumule. 
Fig. 9. Welwitschia mirabilis. Seedling. 
Fig. 10. The same with seed-coat removed. 
Fig. 11. The same with the prcthallus removed in order to show the spade-like foot. 
Figs. 12-17. Different stages in the growth of the seedlings of Gnetum Gnemon. 
Fig. 12. Very young seedling, showing short primary root and the curved hypocotyl, the tip of 
which is still enclosed within the prothallus. 
