EXPLANATION OF THE PLATES. 
57 
Fig. 8-9. Seeds of Op. Engelmanni, var. cyclodes. 
Fig. 10. Seed of Op. occidentalis : One of the embryos, g, shows the cotyledons in an oblique 
almost incumbent position. 
Fig. 11. Seed of Op. angustata. 
Fig. 12-15. Seeds of Op. Camanchica, of different sizes and shapes. 
Pl. XXIII, Fig. 1-5. Seeds of Op. tortispina: 1-3, seeds of different sizes and shapes; 4, 
two embryos in one seed ; g-h, different views of both embryos together as they lay in the seed; 
i, interior layer, and k , exterior smaller embryo ; 5, germination of a double embryo ; two 
young plants from one seed, the larger one still bearing the shell of the seed. 
Fig. 6. Seed of Op. fusiformis. 
Fig. 7-12. Seeds of Op. Rafinesquii, and some of its varieties and sub-species ; 7, usual form 
from Missouri, (see pl. X, fig. 3 ;) h, i, 1c, germination in different stages of development; l, 
seedling with three cotyledons. 
Fig. 8. Small seed from the fruit, (represented on pl. X, fig. 4.) 
Fig. 9. Op. stenochila. 
Fig. 10-12. Op. cymochila: 10 and 11, different forms of the usual variety ; 12, seed of the 
variety montana. 
Fig. 13. Seed of Op. vulgaris. 
Fig. 14. Seeds of Op. basilaris : An irregular and a very regular one from the same fruit. 
Fig. 15. Seed of Op. hystricina. 
Fig. 16-19. Seeds of different forms of Op. Missouriensis : 16, var. rufispina 17, var. pla- 
tycarpa ; h, seedling of same ; 18, var. albispina ; 19, var. tricophora. 
Pl. XXIV, Fig. 1-2. Op. Missouriensis: 1, var. with smaller fruit and seeds from the 
Upper Missouri; 2, var. microsperma. (See pl. XIY, Fig. 5-7.) 
Fig. 3. Seed of Op. spilerocarpa. 
Fig. 4. Seed of Op. ertnacea : The embryo, g, shows considerable obliquity of the cotyledons. 
Fig. 5. Seed of Op. fragilis : From the Yellowstone river. 
Fig. 6. Seed of Op. clavata : The embryo, g, oblique. 
Fig. 7. Seed of Op. Parryi: Embryo, g, nearly accumbent. 
Fig. 8. Seed of Op. echinocarpa : One of the seeds quite regular, the other irregular ; embryo, 
g, g, always regularly accumbent; h, and i, seedlings with the very narrow and thick cotyledons 
crossing each other, one of them bearing the shell of the seed. 
Fig. 9-10. Seeds of Op. Whipplei : 9, seed of the plant represented Pl. XVII, fig. 2, seed 
larger, commissure perfectly linear, cotyledons oblique ; 10, seeds of the other specimen, Pl. 
XXIP fig. 1, seeds smaller, of different shapes, commissure a little wider, cotyledons oblique, in 
i somewhat separated; in k three cotyledons, of which l is a transverse section, h, seedling with 
very narrow and long cotyledons. 
Fig. 11. Seeds of Op. acantiiocarpa, of different shapes all from one fruit. 
Fig. 12. Seeds of Op. arborescens, of different shapes belonging to the plant, figured Pl. XVII, 
fig. 5, smaller than those sent by other collectors, embryo g, regularly incumbent. 
Fig. 13-15. Seeds of Op. vaginata : 13-14, seeds of different sizes from the plant, Pl. XX, 
fig. 1., the smaller one is empty and perhaps not fully formed; 15, seed of the same species 
collected in Mexico by Dr. Gregg. Cotyledons regularly incumbent. 
Fig. 16-19. Seeds of Op. frutescens: 16, var. longispina from the Llano Estacado (Pl. XX, 
fig. 2); 17, same from Mexico Dr. Gregg ; 18, same from Williams River branch of the great 
Colorado ; 19, var. brevispina, from Texas, Lindheimer. In all these the cotyledons of the 
embryo are regularly incumbent. 
Fig. 20. Seeds of Op. tesselata : embryo oblique or almost accumbent. 
All the figures are of natural size unless the contrary is expressly stated. They were drawn 
with the greatest accuracy, partly from living and in part from dried specimens, by Mr. Paulus 
Sr 
