the Prothccllus of Equisetum debile , Roxb. 181 
Fig. 20. A female prothallus which has begun to form antheridia. x 2. 
Fig. 21. Another and larger female prothallus with antheridia on the margins, x 2. 
Fig. 22. A female prothallus with a plant growing out of it near the margin. The first lateral 
branch of the main shoot was already two inches in length. The main shoot was still longer, x 2. 
From a shady place. 
Fig. 23. A vertical section through a well-grown prothallus, showing arrangement and general 
outline of lobes. Ar = archegonia. x 20. 
Fig. 24. One of the lobes, x about 70. 
Fig. 25. Vertical section through the marginal part of a prothallus, showing large compact 
portion and small lobe. Roughly, the part above the line is green, that below it is full of starch, but 
contains no chloroplasts. x 20. Ar = archegonia ; = meristem. 
Fig. 26. A lobe from the margin of Fig. 19. Ar = archegonium. The line shows the upper 
level of the compact part of the prothallus. x 20. 
Fig. 27. Horizontal sections of a few lobes at various heights. 
Figs. 28, 29. Mature archegonia in longitudinal section, x 300. 
Fig. 30. Transverse section of the neck of an archegonium. 
Fig. 31. A part of the prothallus in vertical section, showing antheridia. x 20. 
Fig. 32. Three antheridia in various stages of development. Vertical section. Pa = para- 
physis. x 300. The spermatogenous cells in this and the two following figures are shaded. 
Fig. 33. A ripe antheridium at the base of a lobe, in vertical section, x 70. 
Fig. 34. An open antheridium seen from above, x 300. 
Fig. 35. A ripe but still closed antheridium seen from above, x 300. 
Fig- 36. Sperm mother-cells showing curved nucleus and blepharoplast. x 1250. a , from a 
complete teased-out cell fixed by osmic acid. 
Fig. 37. Sperm fixed over osmic acid fumes, while swimming, x 1250. The part derived from 
the chromatin and the blepharoplast is shaded. 
Fig. 38. Embryo in longitudinal section, x 300. 
Fig. 39. Complete embryo about a week old. x 40. 
Figs. 40-43. Transverse section of a young plant from the root upwards through the hypocotyl 
to the shoot. 
Fig. 40. Transverse section of root. 
Fig. 41. Formation of a gap and pith. 
Fig. 42. Closed ring of the stele with pith in the centre. 
Fig. 43. Stem structure with separate vascular bundles. The typical endarch structure has not 
yet been established. 
Fig. 44. A large prothallus with fifteen plants growing out of it. Nat. size. 
Fig. 45. A small prothallus with a single, much-branched plant attached to it. The roots have 
been cut short. Nat. size. 
