20 Transactions. 



outward growth of the latter. Thus a basal cell to the archegonium is not 

 formed. In figs. 39, 41, and 42 it will be seen that the large nucleus of 

 the inner cell next divides, and a horizontal wall is formed, this (according 

 to my interpretation) cutting off a neck-canal cell from a central cell. 

 This neck-canal cell seems to be evident in the slightly older archegonia 

 shown in figs. 43 and 46. The neck-cells lengthen considerably, and divide 

 by horizontal walls generally two or three times, so that a straight neck 

 is formed (figs. 15, 45, 46) of three or four tiers of cells. The neck- 

 canal cell pushes up between the neck-cells, and probably divides once or 

 twice in the usual way, although I could not demonstrate this, except 

 perhaps in the instance shown in fig. 45 — much less was a ventral-canal 

 cell to be traced. In fig. 15 is shown the rounded apical head of a small 

 prothallus branch on which two archegonia will be seen with protruding 

 necks. In these cases the neck consists of the lowest tier of cells, which 

 have already taken on the characteristic brown coloration, and an upper 

 tier of elongated cells which will divide again by two or three horizontal 

 walls. As soon as the outermost tier separate the neck-canal becomes 

 conspicuously brown. Sooner or later, after the archegonium has matured, 

 the outer three or four tiers of neck-cells fall off, leaving only the lowest 

 tier, whose walls become strongly cutinized. These cells have already 

 assumed the brown colour in their walls, and their nuclei and contents 

 soon do the same. The exposed horizontal walls of this tier of four cells 

 slope inwards towards the canal in a saucer-like form (fig. 15). Although 

 an occasional old archegonium may be seen on the older parts of the 

 prothallus still showing the full length of neck, yet the characteristic 

 appearance of old archegonia is that just described, the four brown rather 

 peculiarly projecting neck-cells, which originally constituted the lowest 

 tier in the neck, surmounting the brown egg-cell (figs. 47 to 49). A close 

 inspection not infrequently shows the remains of the broken-off cell-walls 

 still attached to the outer surface of these persisting neck-cells. 



The Development of the Embryo. 



Unfertilized old archegonia are abundant on most parts of the main 

 prothallus-body, and are very evident on account of the brown colour of 

 the egg-cell and of the persisting lowest tier of neck-cells. I sectioned 

 a good number of large prothalli on which I found no fertilized archegonia 

 at all, but there were several prothalli on which I found both fertilized 

 archegonia in which the egg-cell had not as yet shown any cell-division, and 

 also several young developing embryos. Also I obtained a number of pro- 

 thalli which bore single young plantlets in various stages of development, 

 while most of the largest prothalli showed the presence of the ruptured 

 cup-like eminence from which a young plant had become detached. Thus 

 although developing embryos do not occur on the prothalli of Tmesipteris 

 as numerously as in certain of the large terrestrial species of Lycopodium 

 prothallus (vide, e.g., Bruchmann, 1898, p. 37), yet it ought to be pos- 

 sible to obtain a complete series. It was to be noticed that in several 

 instances both the fertilized archegonia and also the developing embryos 

 were grouped, whilst one embryo was found close alongside the point of 

 attachment of a young plantlet. Fig. 17 shows a transverse section of 

 a prothallus in which two fertilized egg-cells are to be seen. It may be 

 noted here that I found Delafield's haematoxylin a satisfactory stain for 

 differentiating clearly the young embryos from the surrounding tissue. 

 After fertilization the egg-cell grows considerably in size (figs. 17, 51, 52) 



