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re thus no palaeontological grounds for the hypothesis that the Vascular plants came of a Bryophytic stock； the question of their actual origin remains unsolved。
III。 NATURAL SELECTION。
Hitherto we have considered the palaeontological record of plants in relation to Evolution。 The question remains； whether the record throws any light on the theory of which Darwin and Wallace were the authorsthat of Natural Selection。 The subject is clearly one which must be investigated by other methods than those of the palaeontologist； still there are certain important points involved； on which the palaeontological record appears to bear。
One of these points is the supposed distinction between morphological and adaptive characters； on which Nageli； in particular； laid so much stress。 The question is a difficult one； it was discussed by Darwin （〃Origin of Species〃 （6th edition）； pages 170…176。）； who； while showing that the apparent distinction is in part to be explained by our imperfect knowledge of function； recognised the existence of important morphological characters which are not adaptations。 The following passage expresses his conclusion。 〃Thus； as I am inclined to believe； morphological differences； which we consider as importantsuch as the arrangement of the leaves； the divisions of the flower or of the ovarium； the position of the ovules； etc。first appeared in many cases as fluctuating variations； which sooner or later became constant through the nature of the organism and of the surrounding conditions； as well as through the inter…crossing of distinct individuals； but not through natural selection； for as these morphological characters do not affect the welfare of the species； any slight deviations in them could not have been governed or accumulated through this latter agency。〃 （Ibid。 page 176。）
This is a sufficiently liberal concession； Nageli； however； went much further when he said： 〃I do not know among plants a morphological modification which can be explained on utilitarian principles。〃 （See 〃More Letters〃； Vol。 II。 page 375 （footnote）。） If this were true the field of Natural Selection would be so seriously restricted； as to leave the theory only a very limited importance。
It can be shown； as the writer believes； that many typical 〃morphological characters；〃 on which the distinction between great classes of plants is based； were adaptive in origin； and even that their constancy is due to their functional importance。 Only one or two cases will be mentioned； where the fossil evidence affects the question。
The pollen…tube is one of the most important morphological characters of the Spermophyta as now existingin fact the name Siphonogama is used by Engler in his classification； as expressing a peculiarly constant character of the Seed…plants。 Yet the pollen…tube is a manifest adaptation； following on the adoption of the seed…habit； and serving first to bring the spermatozoids with greater precision to their goal； and ultimately to relieve them of the necessity for independent movement。 The pollen…tube is constant because it has proved to be indispensable。
In the Palaeozoic Seed…plants there are a number of instances in which the pollen…grains； contained in the pollen…chamber of a seed； are so beautifully preserved that the presence of a group of cells within the grain can be demonstrated； sometimes we can even see how the cell…walls broke down to emit the sperms； and quite lately it is said that the sperms themselves have been recognised。 （F。W。 Oliver； 〃On Physostoma elegans； an archaic type of seed from the Palaeozoic Rocks〃； 〃Annals of Botany〃； January； 1909。 See also the earlier papers there cited。） In no case； however； is there as yet any satisfactory evidence for the formation of a pollen…tube； it is probable that in these early Seed…plants the pollen… grains remained at about the evolutionary level of the microspores in Pilularia or Selaginella； and discharged their spermatozoids directly； leaving them to find their own way to the female cells。 It thus appears that there were once Spermophyta without pollen…tubes。 The pollen…tube method ultimately prevailed； becoming a constant 〃morphological character；〃 for no other reason than because； under the new conditions； it provided a more perfect mechanism for the accomplishment of the act of fertilisation。 We have still； in the Cycads and Ginkgo； the transitional case； where the tube remains short； serves mainly as an anchor and water…reservoir； but yet is able； by its slight growth； to give the spermatozoids a 〃lift〃 in the right direction。 In other Seed…plants the sperms are mere passengers； carried all the way by the pollen…tube； this fact has alone rendered the Angiospermous method of fertilisation through a stigma possible。
We may next take the seed itselfthe very type of a morphological character。 Our fossil record does not go far enough back to tell us the origin of the seed in the Cycadophyta and Pteridosperms （the main line of its development） but some interesting sidelights may be obtained from the Lycopod phylum。 In two Palaeozoic genera； as we have seen； seed…like organs are known to have been developed； resembling true seeds in the presence of an integument and of a single functional embryo…sac； as well as in some other points。 We will call these organs 〃seeds〃 for the sake of shortness。 In one genus （Lepidocarpon） the seeds were borne on a cone indistinguishable from that of the ordinary cryptogamic Lepidodendreae； the typical Lycopods of the period； while the seed itself retained much of the detailed structure of the sporangium of that family。 In the second genus； Miadesmia； the seed…bearing plant was herbaceous； and much like a recent Selaginella。 （See Margaret Benson； 〃Miadesmia membranacea； a new Palaeozoic Lycopod with a seed…like structure〃； 〃Phil。 Trans。 Royal Soc。 Vol。 199； B。 1908。） The seeds of the two genera are differently constructed； and evidently had an independent origin。 Here； then； we have seeds arising casually； as it were； at different points among plants which otherwise retain all the characters of their cryptogamic fellows； the seed is not yet a morphological character of importance。 To suppose that in these isolated cases the seed sprang into being in obedience to a Law of Advance （〃Vervollkommungsprincip〃）； from which other contemporary Lycopods were exempt； involves us in unnecessary mysticism。 On the other hand it is not difficult to see how these seeds may have arisen； as adaptive structures； under the influence of Natural Selection。 The seed…like structure afforded protection to the prothallus； and may have enabled the embryo to be launched on the world in greater security。 There was further； as we may suppose； a gain in certainty of fertilisation。 As the writer has pointed out elsewhere； the chances against the necessary association of the small male with the large female spores must have been enormously great when the cones were borne high up on tall trees。 The same difficulty may have existed in the case of the herbaceous Miadesmia； if； as Miss Benson conjectures； it was an epiphyte。 One way of solving the problem was for pollination to take place while the megaspore was still on the parent plant； and this is just what the formation of an ovule or seed was likely to secure。
The seeds of the Pteridosperms； unlike those of the Lycopod stock； have not yet been found in statu nascendiin all known cases they were already highly developed organs and far removed from the cryptogamic sporangium。 But in two respects we find that these seeds； or some of them； had not yet realised their possibilities。 In the seed of Lyginodendron and other cases the micropyle； or orifice of the integument； was not the passage through which the pollen entered； the open neck of the pollen…chamber protruded through the micropyle and itself received the pollen。 We have met with an analogous case； at a more advanced stage of evolution； in the Bennettiteae； where the wall of the gynaecium； though otherwise closed； did not provide a stigma to catch the pollen； but allowed the micropyles of the ovules to protrude and receive the pollen in the old gymnospermous fashion。 The integument in the one case and the pistil in the other had not yet assumed all the functions to which the organ ultimately became adapted。 Again； no Palaeozoic seed has yet been found to contain an embryo； though the preservation is often good enough for it to have been recognised if present。 It is probable that the nursing of the embryo had not yet come to be one of the functions of the seed； and that the whole embryonic development was relegated to the germination stage。
In these two points； the reception of the pollen by the micropyle and the nursing of the embryo； it appears that many Palaeozoic seeds were imperfect； as compared with the typical seeds of later times。 As evolution went on； one function was superadded on another； and it appears impossible to resist the conclusion that the whole differentiation of the seed was a process of adaptation； and consequently governed by Natural Selection； just as much as the specialisation of the rostellum in an Orchid； or of the pappus in a Composite。
Did space allow； other examples might be added。