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ts have not been distinct from the first； though no doubt the great majority of known Gymnosperms； especially the Coniferae； represent branch…lines of their own。
The stamens of the Bennettiteae are arranged precisely as in an angiospermous flower； but in form and structure they are like the fertile fronds of a Fern； in fact the compound pollen…sacs； or synangia as they are technically called； almost exactly agree with the spore…sacs of a particular family of Fernsthe Marattiaceae； a limited group； now mainly tropical； which was probably more prominent in the later Palaeozoic times than at present。 The scaly hairs； or ramenta； which clothe every part of the plant； are also like those of Ferns。
It is not likely that the characters in which the Bennettiteae resemble the Ferns came to them directly from ancestors belonging to that class； an extensive group of Seed…plants； the Pteridospermeae； existed in Palaeozoic times and bear evident marks of affinity with the Fern phylum。 The fern… like characters so remarkably persistent in the highly organised Cycadophyta of the Mesozoic were in all likelihood derived through the Pteridosperms； plants which show an unmistakable approach to the cycadophytic type。
The family Bennettiteae thus presents an extraordinary association of characters； exhibiting； side by side； features which belong to the Angiosperms； the Gymnosperms and the Ferns。
ii。 ORIGIN OF SEED…PLANTS。
The general relation of the gymnospermous Seed…plants to the Higher Cryptogamia was cleared up； independently of fossil evidence； by the brilliant researches of Hofmeister； dating from the middle of the past century。 （W。 Hofmeister； 〃On the Germination； Development and Fructification of the Higher Cryptogamia〃； Ray Society； London； 1862。 The original German treatise appeared in 1851。） He showed that 〃the embryo…sac of the Coniferae may be looked upon as a spore remaining enclosed in its sporangium； the prothallium which it forms does not come to the light。〃 （Ibid。 page 438。） He thus determined the homologies on the female side。 Recognising； as some previous observers had already done； that the microspores of those Cryptogams in which two kinds of spore are developed； are equivalent to the pollen…grains of the higher plants； he further pointed out that fertilisation 〃in the Rhizocarpeae and Selaginellae takes place by free spermatozoa； and in the Coniferae by a pollen…tube； in the interior of which spermatozoa are probably formed〃a remarkable instance of prescience； for though spermatozoids have not been found in the Conifers proper； they were demonstrated in the allied groups Cycadaceae and Ginkgo； in 1896； by the Japanese botanists Ikeno and Hirase。 A new link was thus established between the Gymnosperms and the Cryptogams。
It remained uncertain； however； from which line of Cryptogams the gymnospermous Seed…plants had sprung。 The great point of morphological comparison was the presence of two kinds of spore； and this was known to occur in the recent Lycopods and Water…ferns （Rhizocarpeae） and was also found in fossil representatives of the third phylum； that of the Horsetails。 As a matter of fact all the three great Cryptogamic classes have found champions to maintain their claim to the ancestry of the Seed… plants； and in every case fossil evidence was called in。 For a long time the Lycopods were the favourites； while the Ferns found the least support。 The writer remembers； however； in the year 1881； hearing the late Prof。 Sachs maintain； in a lecture to his class； that the descent of the Cycads could be traced； not merely from Ferns； but from a definite family of Ferns； the Marattiaceae； a view which； though in a somewhat crude form； anticipated more modern ideas。
Williamson appears to have been the first to recognise the presence； in the Carboniferous flora； of plants combining the characters of Ferns and Cycads。 （See especially his 〃Organisation of the Fossil Plants of the Coal…Measures〃； Part XIII。 〃Phil。 Trans。 Royal Soc。〃 1887 B。 page 299。） This conclusion was first reached in the case of the genera Heterangium and Lyginodendron； plants； which with a wholly fern…like habit； were found to unite an anatomical structure holding the balance between that of Ferns and Cycads； Heterangium inclining more to the former and Lyginodendron to the latter。 Later researches placed Williamson's original suggestion on a firmer basis； and clearly proved the intermediate nature of these genera； and of a number of others； so far as their vegetative organs were concerned。 This stage in our knowledge was marked by the institution of the class Cycadofilices by Potonie in 1897。
Nothing； however； was known of the organs of reproduction of the Cycadofilices； until F。W。 Oliver； in 1903； identified a fossil seed； Lagenostoma Lomaxi； as belonging to Lyginodendron； the identification depending； in the first instance； on the recognition of an identical form of gland； of very characteristic structure； on the vegetative organs of Lyginodendron and on the cupule enveloping the seed。 This evidence was supported by the discovery of a close anatomical agreement in other respects； as well as by constant association between the seed and the plant。 （F。W。 Oliver and D。H。 Scott； 〃On the Structure of the Palaeozoic Seed； Lagenostoma Lomaxi； etc。〃 〃Phil。 Trans。 Royal Soc。〃 Vol。 197 B。 1904。） The structure of the seed of Lyginodendron； proved to be of the same general type as that of the Cycads； as shown especially by the presence of a pollen…chamber or special cavity for the reception of the pollen…grains； an organ only known in the Cycads and Ginkgo among recent plants。
Within a few months after the discovery of the seed of Lyginodendron； Kidston found the large； nut…like seed of a Neuropteris； another fern…like Carboniferous plant； in actual connection with the pinnules of the frond； and since then seeds have been observed on the frond in species of Aneimites and Pecopteris； and a vast body of evidence； direct or indirect； has accumulated； showing that a large proportion of the Palaeozoic plants formerly classed as Ferns were in reality reproduced by seeds of the same type as those of recent Cycadaceae。 （A summary of the evidence will be found in the writer's article 〃On the present position of Palaeozoic Botany〃； 〃Progressus Rei Botanicae〃； 1907； page 139； and 〃Studies in Fossil Botany〃； Vol。 II。 （2nd edition） London； 1909。） At the same time； the anatomical structure； where it is open to investigation； confirms the suggestion given by the habit； and shows that these early seed…bearing plants had a real affinity with Ferns。 This conclusion received strong corroboration when Kidston； in 1905； discovered the male organs of Lyginodendron； and showed that they were identical with a fructification of the genus Crossotheca； hitherto regarded as belonging to Marattiaceous Ferns。 （Kidston； 〃On the Microsporangia of the Pteridospermeae； etc。〃 〃Phil。 Trans。 Royal Soc。〃 Vol。 198； B。 1906。）
The general conclusion which follows from the various observations alluded to； is that in Palaeozoic times there was a great body of plants （including； as it appears； a large majority of the fossils previously regarded as Ferns） which ha