104 
PROFESSOR A. ANSTRUTHER LAWSON ON 
condition is represented in fig. 29. The outer wall has the same arrangement as that 
shown in the previous figure, hut the inner part has divided further, and three nuclei 
are visible in this median section. The next stage found is that shown in fig. 30. It 
will be seen that the outer wall cells have increased in number, and that the young 
antheridium bulges out as a rounded protuberance from the surface. The section 
is quite median, and shows six cells, indicating a more advanced division of the 
inner antheridium. Fig. 31 represents a median section showing ten cells of the 
inner region. A still more advanced stage of the same is represented in fig. 32. 
These developmental stages shown in figs. 28 to 32 were quite frequently found 
from sections taken near the growing apex, and they are fair samples of the regular 
development of the antheridium. 
Throughout its entire development the antheridium of Psilotum * bears a very 
close resemblance to Tmesipteris. This is quite evident by comparing the series in 
figs. 28 to 32 with that of figs. 7 to 10. There is, however, one curious difference to 
be noted. In all these stages here represented, and in many others that were 
observed and measured, the antheridium of Tmesipteris is just about twice the size 
of that of Psilotum. 
This difference was not merely in regard to the entire structure of the antheridium, 
but was quite noticeable in the individual cells. If, for instance, we compare fig. 7 
with fig. 28, or fig. 8 with fig. 31, or fig. 9 with fig. 32, it will be seen that this 
difference is cytological as well as structural. These figures were all drawn with the 
same microscope and camera-lucida, and are of the same magnification. It is quite 
clear that the cells and nuclei of Tmesipteris are larger than those of Psilotum. 
It is difficult to understand the reason for this difference. The difference in size of 
the mature antheridia of the two plants is indicated in figs. 12 and 34. 
In regard to the cytological details associated with spermatogenesis, not sufficient 
microtome sections were made for the purpose. I am therefore, as yet, unable to 
say whether blepharoplasts are a feature of spermatogenesis in either Tmesipteris 
or Psilotum. I hope to investigate this detail when material at hand is more 
plentiful. In fig. 33 we have a representation of a median section of a nearly mature 
antheridium. The nuclei of the spermatocytes have undergone a marked change. 
They have become crescent-shaped, or even coiled. They stain very deeply with 
nuclear stains, and are really spermatozoids not quite mature. A surface view of 
the antheridium at this time is represented in fig. 34. Only the wall cells are 
shown, and the arrangement of these into a large spherical envelope is very 
characteristic. A somewhat oblique section of a mature antheridium is represented 
in fig. 35. The coiled, deeply staining, mature spermatozoids are clearly visible. 
* Lang’s (1904) description of the antheridium (on a prothallus provisionally referred to Psilotum) is as 
follows: — “From the few developmental stages observed it was clear that the antheridium originates in the same 
way as that of Lycopodium, the first division separating an outer cell, which forms the wall, from an inner one giving 
rise to the mass of spermatocytes. The outer wall of the mature antheridium is one layer of cells thick, and is nearly 
level with the surface of the prothallus.” 
