40 
Oliver and Salisbury . — On the Structure and 
species L. ovoides , has already been a matter of comment, 1 whilst in Physo- 
stoma no fewer than eighty grains have been counted in a single section that 
recently passed through our hands — a number that may safely be trebled 
to get an approximation to the full number. In Conostoma , with its long 
micropyle, tiny lagenostome, and plinth cavity, the evidence shows that an 
abundance of large pollen-grains found their way into the plinth cavity. 
When regard is had to the relations of the parts in these three types, 
it seems evident that, assuming them to be derived from a common ancestral 
group, the reception of pollen was originally independent of the integument. 
If the free lobing of the integument of Physostonia is an archaic character, 
then in so far as these lobes collectively assisted at pollination this pristine 
method of pollen reception has been lost and an approach made to the 
entire micropyle as found in Conostoma and Gnetopsis. 
In marked contrast with these types was Lagenostoma , where the 
lagenostome had kept pace with the investing members and, by means of 
its elongated neck, retained to itself the function of pollen reception. The 
persistence of this exserted type of lagenostome, a rare condition, may 
perhaps be regarded as a kind of conservatism which militated against the 
surrender to the investing structure of the receptive and conductive 
functions — a conservatism which finds further illustration in Gnetum , where 
the inner integument projects far beyond the envelopes exterior to itself. 
This at any rate seems clear, the arrangements which prevailed in the 
Conostoma type, with its intercalated plinth, had as a result the carriage 
of the pollen deep into the heart of the seed. The double functions of 
reception and storage relinquished by the lagenostome were taken over by 
the micropyle and plinth cavity respectively, the lagenostome persisting as 
a sort of inner vestibule — a mere piece in an elaborate though doubtless 
very perfect mechanism. The very smallness of the lagenostome, whose 
diameter never exceeded 150/^ in the known representatives of this type — 
a dimension barely equalling the length of two pollen-grains as we know 
them in the plinth cavitity — fully accords with this vestigial phase upon 
which the lagenostome would appear to have entered. 
Passing on to the seeds of other groups, we come first to members of 
the Medulloseae, of which Trigonocarpus , Stephanospermum , and a number 
of the French Permo-carboniferous seeds afford the best known examples. 
In these, so far as information is available, there existed a prominent 
nucellar beak which engaged with the base of the micropyle. The pollen 
was received by this tubular beak from the micropyle and passed into 
a deeper lying ‘ pollen-chamber ’ below, perhaps comparable to the plinth 
cavity of Conostoma. The flattened seeds usually referred to the Cordaiteae 
appear to be in substantial agreement, whilst the same remark holds good 
of the living genera of Cycads and of Ginkgo. 
1 Oliver and Scott : loc. cit., p. 214. 
