Riassunto
Excerpt from Index Filicum: A Synopsis, With Characters, of the Genera, and an Enumeration of the Species of Ferns, With Synonymes, References, &C. &C
In the prefixed Synopsis of the Genera, the author has sketched out what appears to him the most intelligible arrangement, as well as endeavoured to simplify the definitions of the generic groups. As regards the genera themselves, it has been an endeavour to hold a middle course, between the excessive sub-division and the equally inconvenient non division of the older genera. The system of classification adopted, is that based upon the joint recognition of (1) the plan on which the vascular structure is developed, and (2) the nature of the fructification. This is the best plan yet devised, and if carried out with moderation, not to excess, and with a well-defined appreciation of what constitutes an important distinction, it is Open to fewer objections and presents fewer difficulties than any other plan which has been suggested. It has nevertheless appeared, that in the application of this system, the number Of genera has been hitherto too much extended; consequently those which are regarded as less ne cessary or most trivially characterized, dependant on the slighter venal and other differences, have not been adopted; while those based on the broader differences of venation, such for instance as are presented by free-veined and net~veined species, and again among the latter such as occur in a uniform or a pinnate plan of reticulation, or in the presence or absence of free included veinlets, have been unreservedly admitted.
The Speeies,will,throughout,be enumerated in alphabetical order, for facility of reference. Not having knowledge of every species it has been his duty to record, the author cannot hepe to have avoided mistakes - sometimes no doubt in combining species which should have been kept separate, but more frequently, in all probability, in keeping separate what should have been united. It is however trusted that he may at leasthave fulfilled a useful task in bringing together and placing in an accessible form, the various names scattered through numerous publications. The tendency of his investigations in this department of the subject, has been to the effect, that many plants of the value of mere varieties - constitutional or geographic, have been hitherto regarded as species; and he is prepared to believe that a more complete acquaintance with the modifications of form resulting from wide distribution, would lead to the combination of plants which he has here left separated. Notwithstanding this, he cannot but think that at the present day the current of Opinion seems to be setting too strongly in this direction, in the disregard which is paid to actual differences - a state of things which, equally with the other extreme, is Opposed to the possibility of defining with precision, and consequently of recognising species.
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