382 



UISr.OVERY 



Osnmndace.T. In all such fossil series the marvel grows 

 tliat these types of vegetation, often so well characterised 

 in xcromorphic organisation, should have been so re- 

 markably constant in general morphology back to remote 

 Pal.TOZoic times, with as little suggestion as to the 

 evolution of their own very special lines as of those of 

 any other type of plant. Tor the causes that produced 

 them one must go far back beyond the Carboniferous ; 

 and while the vegetation of this period is made up of 

 types evidently already relegated to inferior biological 

 stations, as partial aquatics or the vegetation of swamps 

 liable to marine inundations, there is little suggestion 

 as to what may have been the plant-life growing con- 

 temporaneously in forest-formation on better ground, 

 of which no trace appears to have been fossilised. The 

 extent to which fossil botany can ever have anything to 

 say on the question of origins receives emphasis, as the 

 appearance of a type in the fossil state clearly affords 

 little clue to either the locus or the time of its initiation, 

 and pateobotanists are still prone to confuse " first 

 appearance " with " evolution." Thus, Dr. Scott writes 

 (p. 370) : "A remarkable lacuna in our knowledge of the 

 older fossil Filicales is the entire absence, so far as is yet 

 ascertained, of any satisfactory evidence for the existence 

 of heterosporous forms." Yet in other series the seed- 

 habit, as following on beyond the heterosporous con- 

 dition, was already well advanced in trees of the Upper 

 Devonian, as well as in Carboniferous Pteridosperms. 

 The period for the first inception of Heterospory must 

 be very remote, as it is diilicult to believe that such a 

 significant adaptation to subaerial environment was not 

 contemporaneous in all advancing phyla of Land-flora, and 

 that modern Heterosporous Filicineaj must be a mere 

 relic of the many types that have been, whether these are 

 found in the fossil state or not. 



A final section, which is entirely new, will be welcomed 

 by botanists as affording a useful summary of recent 

 publications by Kidston and Lang on the critical types 

 of Rhynia and Hornca, which have been attributed, 

 without any very clear reasons, to Psilophytales, on the 

 lines of Dawson's older genus of Psilophyton {1S59). 

 These plants are classed by Dr. Scott with Pteridophyta, 

 on the assumption that the definition of the latter must 

 include any form in which the sporophyte generation is 

 a plant apparently wholly independent of the gameto- 

 phyte and attached to the soil, however little it may 

 resemble a Pteridophyte in other fundamental features. 

 The plants were growing on peat, presumably formed by 

 their ultimate decomposition, and have been found in 

 the Lower Devonian of Scotland. They are very suggestive 

 of an enlarged moss-habit, only the branches bear spore- 

 capsules, including spore-tetrads, which belong distinctly 

 to the asexual generation. Any light that can be thrown 

 on the vexed question of the extreme dissimilarity of the 

 two generations of the moss life-cycle should be welcome, 

 in view of the fact that the Bryophyta represent the 

 simplest and presumably the most archaic forms of 

 land-flora, and may hence be expected to illustrate more 

 clearly than any other types the biological factors which 

 have led to the successful evolution of land-plants. 



From the general consideration of the modem repre- 

 sentatives of these series, it would appear that the two 

 generations were originally of identical morphological 

 organisation, inheriting a two-phase life-cycle from the 

 higher alga; of the sea ; and that while the moss-capsule 

 has been adjusted to the production and dispersal of air- 

 borne spores, its increasing parasitism on the parental 

 gamctophyte generation has led to a state of decadence 

 and somatic deterioration as a self-supp)orting organism, 

 as illustrated in further degree by the smaller and more 

 wholly parasitic capsules of Hepatica; and Jungermannije. 

 That the modern moss-sporogonium is but a relic of a 

 shoot-system which was once branched and probably 

 leafy, with photosynthetic tissues and stomata, bearing 

 spore-producing end-ramuli in the manner of the 

 antheridial ramuli of the leafy moss-plant, may be 

 accepted, in spite of much older academic si)eculation to 

 the contrary. The general organisation of Rhynia and 

 Ilornea so closely appro.ximatcs that of such an ideal 

 prototype, in their freely branched rhizome-systera with 

 vestigial leaf-points, terminal capsules, and rhizoidal 

 attachment to the peaty soil, that these and a.ssociated 

 types bid fair to be the most critically valuable forms of 

 plant described in recent years since the original accounts 

 of Benneltites and Lyginodendron. 



The fact that Dr. Scott, following Kidston and L,ang, 

 homologises these peat-plants with the saprophytic 

 Psilotum of tropical forests as primitive Pteridoph\-tes, 

 in which progressive sterilisation has not yet given rise 

 to definite leaf-members, and a root-system is not yet 

 invented, as an emendation on the admiration expressed 

 for Lycopodium Selago in the " Land Flora " of Professor 

 Bower, admirably illustrates how plastic are the inter- 

 pretations of such incipient land-flora, and the connection 

 of these ancient lines of moss and fern descent. But it 

 may be pointed out that the discussion of these problems 

 is by no means a question of minor significance to be 

 relegated to the botanical specialist alone. The story of 

 the first evolution of land-plants, even if regarded from 

 no higher an outlook than that of the preparation of the 

 earth's surface for the human race, is one that should 

 interest all representatives of the latter who, in spite of 

 more poetical ways of putting it, are still dependent on 

 subaerial vegetation for their daily bread. 



A. H. C. 



Elementary Notes on Conifers. By A. H. Church, 

 Oxford Botanical Memoirs, No. 8. (Oxford Uni- 

 versity Press, 2s. net.) 

 No. 8 of this useful series, issued by the Oxford 

 Botanical Department, comprises a further instalment 

 of Lecture and Laboratory schedules, arranged more 

 particulariy for a class of Forestry students, and represents 

 the continuation of a first-year course of botany outlmed 

 in preceding memoirs. The schedules are admittedly 

 extremely technical in nature and are full of detail, though 

 abstracted and compressed to a pwint at which they may 

 be unintelligible to the lay mind without considerable 



