20 Campbell . — On the Development of Marat tia. 
Fig. 25. Nearly median transverse section of an older embryo, x 300. 
Fig. 26. A still older embryo in nearly median vertical section. x 100. 
/, cotyledon ; st, stem ; r, root ; ar, archegonium. 
Figs. 27, 28. Prothallia with young plants, x 2. 
PLATE II. 
Fig. 29. Median section of the cotyledon of an embryo of the same age as the 
one shown in Fig. 26. x 300. 
Fig. 30. Vertical section through the stem- apex of a young plant in which the 
second root r 2 was already formed ; x, initial of stem ; tr, first tracheids. x 250. 
Fig. 31. Transverse section of stem-apex with two initials, x x. x6oo. 
Fig. 32. Transverse section through the base of the cotyledon and stem-apex, 
x 100. 
Fig. 33. A stem-apex of the same embryo, x 300. x, the single initial cell. 
Fig. 34. Horizontal section of the lamina of the cotyledon, x 300. 
Figs. 35, 36. Stomata. Fig. 35 surface view. X300. Fig. 36, vertical 
section. x6oo. 
Fig. 37. Cross-section of the lamina of a nearly full-grown cotyledon, passing 
through one of the smaller veins, x 300. 
Fig. 38. Cross-section of the petiole of the cotyledon, x 50. 
Fig. 39. The vascular bundle, x 300. 
Fig. 40. Longitudinal section of root-apex, x, the initial cell, x 3 °°. 
Fig. 41. Transverse section of the apical meristem of the root, x 300. 
Figs. 42-44. Three cross-sections of a root from a young plant, x 250. Fig. 42, 
the apical meristem ; Figs. 43, 44, sections taken lower down. 
Fig. 45. Cross-section of fully developed vascular bundle of the root, x 300. 
Fig. 46. Young plant with persistent pro thallium pr ; natural size. 
