162 
DR JOHN M‘LEAN THOMPSON : A FURTHER CONTRIBUTION 
has been ruptured, and shows the entire course of the annulus. In the majority of 
the small sporangia the stalk consists of three rows of cells, but four-rowed stalks 
have been encountered. 
Typical views of large sporangia are given in text-figs. 8 and 9. These show 
the same general features as are seen in the small sporangia. Size is the only 
point of discrepancy between the two types. The stalk of the large sporangium 
is occasionally four-rowed, and the annulus is commonly very irregular (text-figs. 
10 and 11). The sporangial characters which were previously described have 
accordingly been confirmed. 
The three types of tetrahedral spore already recorded were easily recognisable in 
the new materials (text-figs. 12, 13, 14). The spore-markings were invariably moats 
and irregular channels. Those on the convex sides of the spores were deep and 
broad (text-fig. 15), while those on the remaining triangular surfaces were narrow 
and shallow (text-fig. 16). Many mature spores of each type were seen in section. 
The spore-wall was invariably remarkably thick, and was differentiated into two 
zones of approximately equal breadth (text-fig. 17). A. protoplasmic lining was the 
only recognisable content of any spore. It follows that while the spores are still 
within the sporangia, the only recognisable distinction between the three spore- 
types is one of size. 
The majority of the spores in any small sporangium were of the smallest type, 
but an admixture of intermediate or large spores was also shown. This may be 
illustrated by a table in which are set down the spore-output per sporangium, and 
the number of small, intermediate, and large spores actually present in certain of the 
small sporangia :■ — 
Total Number 
of Spores present in 
the Sporangium. 
Number 
of Small Spores 
present. 
Number of 
Intermediate Spores 
present. 
Number 
of Large Spores 
present. 
32 
32 
0 
0 
32 
31 
0 
1 
31 
31 
0 
0 
31 
28 
3 
0 
30 
30 
0 
0 
29 
29 
0 
0 
29 
27 
0 
2 
29 
27 
-2 
0 
28 
28 
0 
0 
28 
13 
15 
0 
27 
27 
0 
0 
19 
12 
6 
1 
17 
17 
0 
0 
17 
12 
4 
1 
16 
6 
10 
0 
16 
0 
16 
0 
9 
7 
0 
2 
