Added: Veroncia Creamer - Date: 05.11.2021 10:05 - Views: 35926 - Clicks: 4716
Internet Archive's 25th Anniversary Logo. Search icon An illustration of a magnifying glass. User icon An illustration of a person's head and chest. up Log in. Web icon An illustration of a computer application window Wayback Machine Texts icon An illustration of an open book.
Books Video icon An illustration of two cells of a film strip. Video Audio icon An illustration of an audio speaker. Audio Software icon An illustration of a 3. Software Images icon An illustration of two photographs. Images Donate icon An illustration of a heart shape Donate Ellipses icon An illustration of text ellipses. PREFACE While embodying in this book the which I have accumulated during the past twenty years, I should like to take the opportunity of thanking the many friends who have assisted me.
The first to do so were Mr. Carruthers and Professor A. Nathorst, whose work, in fact, led me to undertake these studies. In the troublesome work of determining the plants I have been greatly aided by the constant courtesy and assistance of the officers of the Botanical Department of the British Museum, especially of my friends Mr. Baker and Mr. At Kew also I have received every facility for the work, and to Mr. Baker, the late keeper of the Herbarium, I owe much. Messrs, G.
Groves have also assisted me at various times with specimens of recent plants which I was unable to obtain for myself, and others have been received from friends whose names are too numerous to mention. With regard to the geological material that I have obtained from others, specimens have been vl Preface, received from so many sources that I must leave the reference at the head of each locality to speak for itself, only acknowledging the special aid that has been given by Mr. James Bennie, in collecting the plants of the ancient silted-up lakes of the Scottish Lowlands.
But it soon became obvious that, in order to obtain any satisfactory knowledge of the subject, it was necessary to collect and study the ripe seeds and fruits of our British plants, and to devote much of my leisure to the work of comparison ; fossil seeds had seldom been collected in this country, and recent plants with perfectly ripe seeds were seldom to be found in our herbaria.
From a study of the plants of the Cromer Forest-bed, the work gradually expanded into an examination of any Newer Tertiary plants that could be found in Britain, and as during the past twenty years my employment on the Geological Survey of England has necessitated a close scrutiny of our Newer Tertiary deposits, especially in the south and east of England, I have been brought continu- ally face to face with the problems of the origin of our B 2 Origin of the British Flora.
Moreover, this life spent principally in field, and moor, and forest has forced me to observe how each changing season is marked by corresponding adaptations in the animals and plants, such as enable the species to preserve themselves, to multiply, and to spread ; or, if adaptation fails at any point, through some climatic irregularity, how sweeping and rapid may be the extermination of all except some few accidentally favoured individuals. While col- lecting seeds and fruits for comparison with the fossils I was compelled particularly to observe their many adaptations for dispersal, and also their times of ripening, and the abundance or scarcity of ripe seeds.
It was impossible under such circumstances to avoid seeing the close connexion which must exist between the present geographical distribution of plants and animals and bygone changes in climate and in physical geography. Much of his reasoning was fallacious. To explain the presence of Arctic and of Iberian plants in Britain, he showed that outliers of the Arctic flora stranded on our mountain peaks could be ed for by an appeal to the climatic conditions of former days, when a similar flora covered the whole of our Islands, and was not confined to isolated mountains.
Either might be true, but scarcely both ; for the Irish and Cornish plants are not such as could survive a colder climate like that postulated by Forbes to explain the migration of the Arctic species. We have obtained direct evidence, since Forbes wrote, that all Ireland was at one time strongly glaciated, and also that Arctic plants once occupied the lowlands of Devonshire. This problem of the origin of our flora is one which can be solved, I think, by the historical method, and that seems to be the proper mode of attacking it.
No doubt the imperfection of the geological record is so great as to make the task an exceedingly difficult one ; for nowhere have we yet discovered a continuous sequence of deposits, all fossiliferous, such as would give a connected history of our recent animals and plants from their first appearance in Britain to the present day. The exact order of succession of the deposits, of the physical changes, of the climatic alternations, and of the waves of migration, is still uncer- tain ; though a definite historical record is gradually being built up by the comparison and correlation of numerous overlapping chronicles, each recording at most some three or four of the subordinate stages or periods.
This work of correlation, as already mentioned, has been greatly facilitated by a detailed examination of extensive areas, and a close study of the geology of the more recent deposits.
In this way I have been enabled to trace the connexion between the strata, and often to speak with confidence as to the date of groups of fossils which otherwise would have had to remain as isolated finds. My own researches have been largely aided and supplemented by the examination of material obtained from friends working in districts which I 4 Origin of the British Flora. This has especially been the case with regard to the lacustrine deposits of the Scottish Lowlands, so minutely examined by Mr.
James Bennie. The of these investigations will be found summarised in Chapters IV. In the examination of our recent flora I have looked at the plants mainly from the point of view of the field- naturalist. Their climatic and geographical distribution ; the periods of ripening, and the means of dispersal of their seeds ; their competition with other plants ; and their dependence on, or destruction by animals, were the circum- stances especially noted — more so than critical distinctions of varieties and sub-species.
Not that these distinctions are considered unimportant, but mainly because of the difficulty of studying them without a complete herbarium, too heavy to transport during constant changes of station. Moreover, botanists have almost ignored the essential distinction between a varietal form due to local conditions, and a true sub-species or race ; for many of our named sub-species have evidently no more claim to such rank than have luxuriant garden specimens.
Mitten tells me that seeds gathered by him grew in his garden into the common erect form of broom.
A botanical visit to the Dingle Promontory, in Kerry, in company with Mr. Edmund Baker, produced several instances of this sort. We examined Saxifraga umbrosa and its allied Introduction, 5 forms, of which we found several, each occupying well- defined small areas, and apparently possessing definite characters.
But, as more and more of the patches were examined, these distinctions were found to melt away ; for each fresh patch yielded a slightly different form, so that finally we were able to obtain a nearly complete series of intermediates seeming to connect the extreme kS. Geum, all of them living within a small area under similar conditions.
Pinguicida vulgaris and P. In this case the allied forms, some- times only ranked as sub-species, are both good species, and have different geographical distributions, though they over- lap at more than one point. Botanical books are full of similar anomalies, often due to a natural desire to announce the discovery of a form new to Britain ; but for the student of geographical distribution varietal names founded on such material are worse than useless.
For they tend to confound sub-species, which, if found in isolated areas show, in all probability, a transportation of the seeds from one to another, with varieties or forms, which will reappear wherever the parent species is subject to particular con- ditions. A flora like that of the British Islands may be studied in so many different ways, that it will be well to define at once the standpoints from which it is viewed in the following s. I do not propose, nor do I feel competent, to touch on the questions of the evolution of the species, or of their relationship to each other ; what will be attempted in Chapter Chapter III.
Finally, I propose to give an historical of each species as far back as geological evidence will yet allow it to be traced. It may be considered presumptuous to attempt such a task ; but, though the following Chapters are most imper- fect, yet they may do good by directing attention to lines and methods of research which are as yet little appreciated. The section on the geological history of our flora, being a record of the actual distribution in space and time of our plants from direct observation, will perhaps be the one to which botanists will most readily turn.
Though the present volume is professedly occupied with a discussion of the origin of the British flora, it should not be forgotten that in questions of geographical distribution it is impossible to separate animals from plants, for many plants are directly dependent on certain animals for means of dispersal. Moreover, certain animals are dispersed by the same means as flowering plants, have the same difficul- ties to contend with, are no less dependent on climatic conditions, and are almost equally tied to a single spot during the lifetime of the individual.
The land mollusca in particular are in these respects so like the more sedentary species of flowering plants that I have not hesitated to speak of them where they help to illustrate the subject under consideration.
Beetles, I believe, would also be of use ; but of this order I have unfortunately no knowledge, Introduction. Fresh- water mollusca, freshwater fish, and amphibia seem to obey the same laws of geographical distribution as aquatic plants : the species are usually of wide range, provided the barriers are not excessively broad or high, and the climatic conditions are suitable.
The geological sketch has been greatly condensed ; for it is obviously impossible to deal with so complicated a subject in a limited space, and all that can be done is to give some indication of the climatic conditions, local peculiarities, and character of the flora at each spot where plant-bearing deposits are found. The thorny subject of bygone alternations of climate is perforce discussed, for it lies at the root of our inquiry, I have also been obliged to deal with another equally vexed question, the submer- gence or elevation of the land in Pleistocene times; for this obviously has a most important bearing on the possible survival of plants within our Islands.
In discussing the past climatic changes, while giving the preference to the evidence derived from remains of plants belonging to existing species, I have not hesitated to supplement this by an appeal to other groups of organisms, or to inorganic geology ; for an assemblage of Arctic mammals, a group of Arctic or desert mollusca, a morainic deposit, or erratics brought by floating ice in an Arctic sea, are as good evidence of climate as a group of plants, and are often discoverable in strata in which no plants are preserved.
Secondly, that Britain is not by any means simply an outlier of the continent of Europe. Its flora is an insular one of peculiar character, unlike that of any part of Europe, and unlike that of an oceanic Island. Few, if any, of the species are confined to Britain ; but the Islands contain a selection of the continental species best adapted for dispersal, and best able to hold their own in a changing climate.
Britain, within the lifetime of existing species, has been subjected to many fluctuations of climate, which have left their mark on the flora. On these fluctuations was superimposed a series of orographic changes, such as must have tended greatly to modify local conditions, and must sometimes have aided, sometimes have hindered, the dispersal of the seeds.
The following s deal, therefore, with an insular flora of exceptional type ; in the building up of which selection and sweeping extermination have played so vigorous a part, that the flora now consists largely of an assemblage of the more readily dispersed of the Palaearctic species. Time has not permitted any large amount of variation or formation of sub-species in these Islands ; and in this our flora is totally different from the more ancient floras of oceanic islands, which were beyond the reach of such violent climatic fluctuations as have afiected Britain.
There is one point which needs explanation before we proceed further. I have been obliged in the following s to go back to the popular and original use of the term ' seed. Of the two senses the popular one seems to be by far the most useful scientifically, for it refers to the thing that is sown, not to an embryo with or without Introduction. A seed, therefore, for our present purposes is the one-seeded unit of dispersal. All our British fruits, with the single exception of that of the Cornel, divide into such one-seeded portions, which tend to be dispersed separately, so that the young plants do not interfere with each other.
These units may be seeds in the strict botanical sense, or they may be complete one-seeded fruits ; sometimes they are stones or carpels, one-seeded, or at any rate with only one of the seeds properly developed ; in other cases they include the dried calyx, or other parts of the flower or receptacle. Constant explanation would be needed if an attempt were made to define botanically what part of the fruit is referred to in each case — it is more convenient to accept the perfectly understood popular usage.
The Present Flora of Britain. When the British Flora is carefully studied, it is found to be composed of numerous elements, and can be divided into several well-marked groups. The grouping of the species, however, varies according to the point from which they are viewed. No one of these methods will enable the plants to be grouped into 'provinces' satisfactory for all purposes. Each set of conditions overlies and modifies the distribution which either of the others alone would tend to bring about.
If we begin with the broadest classification, that based on climatic conditions, we find at once that this is not merely a question of average, or of extreme temperature.Dating personals Vernitsa
email: [email protected] - phone:(456) 244-7266 x 3884