30 



Fern, Davallia aculeata. The stem has in its structure a good deal 

 in common with a recent Cycadaceous stem, but the leaves, in 

 structure as well as in form, are of the fern-type. This is the one case 

 among the seed-ferns in which the pollen-bearing organs are well 

 known. They were discovered by Mr. Kidston five years ago. 

 There is no separate stamen ; the little round leaflets, bearing the 

 pollen-sacs on their under surface, form part of the ordinary frond. 

 No doubt the reason why it is so difficult to recognise the male 

 fructifications in these plants is that we are apt to confuse them 

 with the fertile fronds of true ferns. The Lyginodendron type of 

 pollen-bearing organ was known long before Mr. Kidston's dis- 

 covery, but was always regarded as the fructification of a fern. 



The seeds of Lyginodendron were the first to be recognised in 

 any seed-fern. Although they have not, in the species L. oldhamium^ 

 been found in connection with the plant, their identification is 

 beyond doubt, for the husk of the seed bears peculiar glands, 

 identical with those on the leaves and stem of the plant itself, the 

 two also occurring in association. The seeds are small, about a 

 quarter of an inch long, and each is enclosed in the husk or cupule 

 which bears the glands just mentioned. It has been suggested by 

 Sir Joseph Hooker that the glands, like the nectaries of flowers, 

 may have had a relation to the contemporaneous insect life — a 

 suggestion of the utmost interest, though not susceptible of proof. 

 The seed itself has a complicated structure, excellently preserved, 

 which need not be further described, beyond mentioning the peculiar 

 pollen-chamber, which has a column of tissue rising up in the 

 middle, limiting the space for the pollen-grains to a narrow annular 

 crevice. 



Other seeds of the same type have been found attached to 

 branched stalks, which no doubt formed part of the frond. In 

 some cases numbers of empty cupules, from which the seeds 

 appear to have been shed, are borne on naked branches of the frond. 



So far as we know, it was characteristic of the seed-ferns that 

 both kinds of reproductive organs were borne on fronds which were 

 otherwise ordinary vegetative leaves. In this respect these plants 

 were on no higher level than the ferns themselves and so far betray 

 a primitive organisation, complex as their structure was in many 

 ways. As we have seen, there is an approach to this state of 

 things in the female plant of Cycas, with its leaf-like, stem-borne 

 carpels. 



Another form of Palaeozoic seed may be mentioned, which has 

 much in common with that of Lyginodendi'on and may have 

 belonged to some relative plant. As is well known, seeds have 

 an opening or micropyle, in the seed-coat, through which the pollen- 

 grains or their tubes are admitted. In the seed referred to 

 ( Physostoma), the ordinary micropyle is replaced by an arrange- 

 ment which may be compared to the mouth of a lobster-pot. The 

 entrance to the seed is guarded by a ring-fence of rods or tentacles, 

 quite separate from one another, but standing sufficiently close to 



