ANATOMY AND AFFINITY OF CERTAIN RARE AND PRIMITIVE FERNS. 387 
there is a third condition. In this an admixture of large and small spores, or of 
large and intermediate spores, or of small and intermediate spores is found. The 
following are examp 1 es of the analysis of spore-numbers in this exceptional type : — 
Small 
Intermediate 
Large 
Total Spore- 
Spores. 
Spores. 
Spores. 
number. 
15- 
15 
8 
14 
22 
14 
10 
24 
20 
8 
28 
6 
22 
4 
32 
24 
20 
2 
46 
33 
27 
60 
58 
1 
59 
64 
64 
In AT. nivea, Desv., the sporangial construction resembles that of N. affinis, but 
the obliquity of the annulus and its separation from the stalk are more prominent 
Text-fig. 26 . 
than in the latter (figs. 66, 67, 68). The spores are of a uniform tetrahedral type 
and of constant size (fig. 69), and the typical spore-count is 24. 
A more advanced condition is found in N. distans, E. Br. (figs. 77, 78, 79). The 
annulus is usually almost vertical, but the stomium may be directed past the stalk, 
and irregularities in the lignified series occur. The spores are uniformly large, and 
number 12. 
In N. sinuata (Lag.), Klf., the annulus is regular and vertical (fig. 64). The 
spores are of uniform type and size (fig. 65), but their number varies between 32 
and 16. This variation appears to be partly referable to differences in sporangial 
size. 
In these species the sporangia are relatively small. The spore-numbers range 
from 64 to 12, and the annulus is of variable position and form. A general separa- 
tion of the annulus from the stalk is noticeable throughout, and the form of the 
unlignified cells does not suggest that the annulus has ever reached the stalk. 
But in N. trichomanoides (L.), E. Br., the sporangia are large, and the annulus 
— though occasionally regular and perfectly vertical — is typically irregular. It 
reaches the stalk and is interrupted by it (figs. 80, 82, 83, 84). The spores are, 
as in the other species' considered, tetrahedral (fig. 81), and the spore-count appears 
to be 48. 
TRANS. ROY. SOC. EDIN., VOL. LII, PART II (NO. 14). 
60 
