370 
DR JOHN M'LEAN THOMPSON ON THE 
given in figs. 11, 12, 13, 17, the annulus is vertical and interrupted by the stalk. In 
the majority of the sporangia examined the annulus is regular, and meets the stalk 
at the back of the capsule. The main indurated series consists of about twenty cells, 
and the stomium of from six to twelve. The details of construction of the stomium 
are very variable ; the majority of the cell-walls are unlignified, and there is an 
absence of uniformity in number and position of those which are thickened. The 
irregular annulus is typically sinuous, and comprises fewer cells than the regular 
annulus. These features are demonstrated in figs. 18, 19, 2'0, which represent opened 
sporangia. The irregularities may occur at any point in the annulus. In some cases 
additional indurated cells are in the main series (figs. 18, 19) or in the stomium 
(fig. 13), in others the continuity of the lignified series is broken (fig. 14), or con- 
secutive cells differ greatly in size and form (figs. 18, 20). The sporangia with 
irregularities in the annulus give no structural indication of mal-nutrition. They are 
of average size, and their spores are fully matured. The highest spore-count which 
has been recorded was made from a sturdy sporangium with an irregular annulus. 
It seems improbable that these irregularities of the annulus are chance occurrences 
expressive of irregular nutrition or mechanical interference during development. 
The frequency of these irregularities may be gauged from the following analysis. 
100 sporangia from each of six plants were examined ; in 450 the annulus was regular, 
in 150 irregular. The numbers for the individual plants were : — 
1st plant 
2nd „ 
3rd .. 
4th ,, 
5th ,, 
6th ,, 
Sporangia with 
Regular Annulus. 
71 
83 
64 
79 
87 
66 
Sporangia with 
Irregular Annulus. 
29 
17 
36 
21 
13 
34 
It is believed that in J amesonia — as in other plants dealt with in these pages — 
irregularity of form and construction of the annulus is not to be regarded as a chance 
abnormality, but as a characteristic feature worthy of fuller recognition in a phyletic 
discussion. The condition may be considered an upgrade one, the sporangia being 
generally on an upgrade footing as regards form and position of the annulus, but the 
latter has not yet settled down as a uniform advanced type. The existing irregu- 
larities need not be interpreted as reminiscent of the ancestral condition, but they 
point to changes in construction through which the regular vertical annulus may 
have arisen. 
Spores . — As will be seen from figs. 15, 16, the spores are tetrahedral, and smooth- 
walled except for certain fine striations on the triangular faces. They are of uniform 
size. Spore-counts have been made from mature sporangia, and such numbers as 
56, 58, 63, 64, 66, 69, 71, and 72 have been recorded. 56 is the smallest number 
