Hollow ay. — The Prothallus and Young Plant of Tmesipteris. 21 



Fig. 51. — Longitudinal section of fertilized archegonium. X 175. 



Fig. 52. — Longitudinal section of two fertilized arehegonia, in one of which segmentation 

 has begun. X 175. 



Fig. 53. — Longitudinal section of very young embryo, showing earliest segmenta- 

 tion. X 175. 



Fig. 54.— Median longitudinal section of young embryo. X 137. 



Fig. 55. — Median longitudinal section of young embryo. X 137. 



Fig. 56. — Tangential longitudinal section through upper portion of same embryo as 

 shown in fig. 55. X 137. 



Fig. 57. — Median longitudinal section of young embryo. X 137. 



