THE PALEOZOIC SEED LAGENOSTOMA OVOIDES. 485 
В. 46) show beautifully the torn cell-walls, and it is difficult to explain 
these appearances on the degeneration hypothesis. It seems to me highly 
probable that the wall, with its strongly thickened bars, was hygroscopic, and 
split from the central soft tissue with alteration in atmospherie humidity. 
If this were the case, since the wall is never itself ruptured, there must have 
been considerable increase in its circumference. This is, however, allowed 
for by the curved outer walls. For example, let us consider the Manchester 
specimen, since this has the double advantage of being cut transversely 
across the middle of the lagenostome, and of showing the structure of the 
wall remarkably well. Now the circumference of the wall in its present 
collapsed condition is 1:9 mm., but if its radius were to be extended by (say) 
80 ш (i.e. so that a pollen-grain could easily get in at any point) *, the 
circumference would have to be increased to 2:5 mm. If, however, the 
curved outer walls were straightened out, the cireumference would reach 
2-8 mm., so that there is no trouble on this score. But if the wall expanded 
to its full extent, or even considerably less than that, it could not remain 
cireular, because it would almost immediately encounter the cusps of the 
canopy lining. This possibly explains the bevelled wall of the lagenostome, 
which to my mind is not an inherent structural feature, but is impressed 
upon the wall by its close contact with the hard canopy lining during 
expansion. The fact that the wall is not so bevelled lower down, where it 
has plenty of room to expand in the sinus between it and the canopy, 
supports this view. 
Coulter and Chamberlain state that the pollen-chamber is formed from 
below upwards, basing their view apparently on a single section (figured p. 34) 
where the central cone is free from the wall below, but in contact, and pre- 
sumably in continuity, above. In the University College Collection there are, 
however, sections which, while not so good in some respects, are similar in 
that the central cone is to all appearance united to the wall above and free 
below. But these sections (e. g., В. 43, В. 56) contain pollen, which, while 
it does not prove that the dehiscence was not in the affirmed direction, shows 
that an appearance such as that described is fallacious as evidence of the fact. 
Before seeing their account of Lagenostoma, I had come to the conclusion 
that the pollen-chamber was very likely formed from below upwards. This 
view is based on the consideration that the plinth was probably concerned in 
dehiscence. It will be remembered that the structure of this organ is similar 
to that of the lagenostome wall, and, since it is firmly united to the canopy, 
the smallest hygroscopie contraction would immediately rupture its connection 
with the central cone, especially as the curved fibres would tend to straighten 
* Assuming that the central cone nearly touched the wall, as it does normally. In this 
specimen it has been dragged down, and is therefore of much smaller diameter than 
the wall. 
