Index . vii 
b. Figures. page 
i . Diagrammatic view of section of young ovule of Gnetum Gnemon, 3 mm. long, in 
which closure of micropyle is just beginning (M. G. Thoday) .... 38 
2. Drawn from mature seed of G. Gnemon, 3 cm. long (M. G. Thoday) ... 42 
3. The apex of another mature seed of G. Gnemon (M. G. Thoday) .... 43 
4. G. funiculare. Cross-section of apex of seed, showing two bands of fibres in outer 
covering, 4-lobed stony layer of middle covering, and lignified micropylar tube 
(M. G. Thoday) 47 
5. Apex of seed of Bennettites Morierei (from Lignier, 1894, relettered for purposes 
of comparison) (M. G. Thoday) 50 
Diagram of leaf- base of Osmundites Kidstoni, sp. nov., showing the position of the 
meristele and sclerotic tissues (Stopes) 57 
1. Side view of flower of Incarvillea Delavayi (slightly reduced) (Cutting) . . 63 
2. a. Anther-lobes of longer stamen, b. Back view of shorter stamen, c. Young 
stigma. D. Diagrammatic view of flower from above (with a slit in the side). 
e. Diagrammatic longitudinal section of flower. F. Diagram of anther showing 
the pad touching the style (Cutting) 64 
3. Pollen-grains of I. Delavayi, a-f, and of I. grandiflora, g-l (Cutting) . . 68 
1-3. 1. Telephragmoxylon. 2. Brachyoxylon. 3. Picea. Origin of parenchyma 
(Torrey) 75 
1. Method of estimating leaf areas (Gregory) 93 
2 > 3* >> u it >> ........ 95 
4. Curves of increase in the linear dimensions of a leaf (Gregory) . . . .101 
5. Ditto in area of third leaf, June 1917 (Gregory) 102 
6. Ditto in total leaf surface, March 1917 (Gregory) 103 
7. Ditto, June 1917 (Gregory) 104 
8, 9. Growth in area of cotyledons and leaves under two lamps and one lamp respectively 
(Gregory) 108 
10. Curve of increase in leaf surface under two lamps and one lamp respectively 
(Gregory) 111 
11. Equations of curves of closest fit, March, June (Gregory) . . . . .114 
12. Showing for each day the actual areas of successive leaves from the cotyledons 
onwards (Gregory) 115 
13. Curve of increase in total leaf surface, December 1916 (Gregory) . . . 116 
14. Equation of curve of closest fit, December 1916 (Gregory) 117 
15. Equations of curves of closest fit for two lamps and one lamp (Gregory) . .119 
1 . a. Gametophytes of Botrychium obliquum, Miihl, some with attached sporophytes. 
B. Young sporophyte with expanded cotyledon, attached to the gametophyte 
(Campbell) 142 
2. A. Median section of an antheridium just before the final division of the spermatocytes. 
B. Empty antheridium. c. Surface view of antheridium with triangular oper- 
cular cell. d. Surface view of antheridium with two opercular cells (Campbell) 143 
3. A. Young archegonium. b-d. Older archegonia. E. Mature archegonium, 
showing apparent ventral canal cell. F. Open, but unfertilized, archegonium 
(Campbell) . .145 
4. A. Recently fertilized archegonium containing unicellular embryo, b-d. Older 
unicellular embryos (Campbell) 146 
5. A. Archegonium containing much elongated unicellular embryo, b. First division 
in the embryo, c. An older stage, d. Two sections of an older embryo 
(Campbell) 146 
6. a-d. Four of a series of sections of a young embryo, e. Three similar sections 
of an older embryo in which the cotyledon and root are already evident 
(Campbell) 148 
7. A. Two longitudinal sections of an embryo, cut in the plane of the cotyledon. 
B. Two sections of a similar embryo, cut in a plane at right angles to that of a. 
c. Somewhat oblique section of an older embryo showing the conspicuous sheath 
at the base of the cotyledon (Campbell) . 150 
