16 



Transactions. 



organs was concerned. Some of the material was sectioned by the micro- 

 tome, but I found that it showed a tendency in the older regions to resist 

 infiltration by the paraffin. I was inclined to ascribe this to the very dense 

 nature of the fungal element. The prothalli of Tmesipteris are so firm and 

 large that I decided to hand-cut a number of prepared specimens (having 

 no lack of material) in order to supplement my serial sections with others 

 to as great an extent as possible. I found that, on the whole, the hand-cut 

 sections gave good results, being free from the shrinkage so often associated 

 with the microtome sections. Moreover, they took the stain better. The 

 obvious disadvantage of the hand-cut sections is that they are not kept in 



Fig. 18. — Portion of main limb of prothallus in tangential longitudinal section, 



showing archegonia. X 70. 

 Fig. 19. — Portion of main limb of prothallus in transverse section, showing meri- 



stematic activity underneath the epidermis, x 137. 

 Fig. 20. — Transverse section of apex of prothallus. showing single apical cell. X 137. 

 Fig. 21. — Longitudinal section of apex of slender limb of prothallus, showing single 



apical cell. X 137. 



proper sequence. I used throughout Delafield's haematoxylin as a stain, 

 combining it with safranin for the vascular tissues. This haematoxylin 

 was very satisfactory, especially for differentiating the young embryos. 

 However, this method of staining failed to show anything of the process 

 of spermatogenesis. Campbell (1911, p. 28) recommends using the com- 

 bination stain safranin and gentian violet for this purpose, as, indeed, 

 generally for prothallial work. 



In detecting the youngest stages in the development of the sexual 

 organs one is guided by the fact that they occur in close association with 

 others and also with slightly older organs, and also by the greater size of their 



