Definition: division of animals or plants, below a family and above a species
Definition: division of animals or plants, below a family and above a species
Sentences Containing 'genus'
answered the abbe,``man is but man after all, and you are about the best specimen of the genus I have ever known.
So with plants, the seeds of the different varieties of the bean or maize probably differ more in size than do the seeds of the distinct species in any one genus in the same two families.
This seemed to be true, so long as a genus was imperfectly known, and its species were founded upon a few specimens, that is to say, were provisional.
In these remarks on predominence, it should be understood that reference is made only to the forms which come into competition with each other, and more especially to the members of the same genus or class having nearly similar habits of life.
Where many species of a genus have been formed through variation, circumstances have been favourable for variation; and hence we might expect that the circumstances would generally still be favourable to variation.
And this certainly holds true if varieties be looked at as incipient species; for my tables clearly show, as a general rule, that, wherever many species of a genus have been formed, the species of that genus present a number of varieties, that is, of incipient species, beyond the average.
All that we want to show is, that where many species of a genus have been formed, on an average many are still forming; and this certainly holds good.
No naturalist pretends that all the species of a genus are equally distinct from each other; they may generally be divided into sub-genera, or sections, or lesser groups.
How do those groups of species, which constitute what are called distinct genera and which differ from each other more than do the species of the same genus, arise?
Let (A) be a common, widely-diffused, and varying species, belonging to a genus large in its own country.
These two species (A and I), were also supposed to be very common and widely diffused species, so that they must originally have had some advantage over most of the other species of the genus.
And the two or more parent-species are supposed to be descended from some one species of an earlier genus.
And the two new families, or orders, are descended from two species of the original genus; and these are supposed to be descended from some still more ancient and unknown form.
As it is extremely common for distinct species belonging to the same genus to inhabit hot and cold countries, if it be true that all the species of the same genus are descended from a single parent-form, acclimatisation must be readily effected during a long course of descent.
When a part has been developed in an extraordinary manner in any one species, compared with the other species of the same genus, we may conclude that this part has undergone an extraordinary amount of modification since the period when the several species branched off from the common progenitor of the genus.
This relation has a clear meaning on my view: I look at all the species of the same genus as having as certainly descended from the same progenitor, as have the two sexes of any one species.
It might further be expected that the species of the same genus would occasionally exhibit reversions to long-lost characters.
In the horse we see this tendency strong whenever a dun tint appears--a tint which approaches to that of the general colouring of the other species of the genus.
And we have just seen that in several species of the horse genus the stripes are either plainer or appear more commonly in the young than in the old.
Call the breeds of pigeons, some of which have bred true for centuries, species; and how exactly parallel is the case with that of the species of the horse genus!
But whenever we have the means of instituting a comparison, the same laws appear to have acted in producing the lesser differences between varieties of the same species, and the greater differences between species of the same genus.
I have met with striking instances of the rule in the case of varieties intermediate between well-marked varieties in the genus Balanus.
The castes, moreover, do not generally graduate into each other, but are perfectly well defined; being as distinct from each other as are any two species of the same genus, or rather as any two genera of the same family.
For the workers of Myrmica have not even rudiments of ocelli, though the male and female ants of this genus have well-developed ocelli.
In the genus Hippeastrum, in Corydalis as shown by Professor Hildebrand, in various orchids as shown by Mr. Scott and Fritz Muller, all the individuals are in this peculiar condition.
Even within the limits of the same genus, for instance in Dianthus, these two opposite cases occur.
In the same family there may be a genus, as Dianthus, in which very many species can most readily be crossed; and another genus, as Silene, in which the most persevering efforts have failed to produce between extremely close species a single hybrid.
Even within the limits of the same genus, we meet with this same difference; for instance, the many species of Nicotiana have been more largely crossed than the species of almost any other genus; but Gartner found that N.
Although many distinct genera within the same family have been grafted together, in other cases species of the same genus will not take on each other.
The pear can be grafted far more readily on the quince, which is ranked as a distinct genus, than on the apple, which is a member of the same genus.
If the extreme forms in the genus happen to have been thus destroyed, the genus itself will stand more distinct from other allied genera.
The Silurian Lingula differs but little from the living species of this genus; whereas most of the other Silurian Molluscs and all the Crustaceans have changed greatly.
No fixed law seems to determine the length of time during which any single species or any single genus endures.
Thus, as I believe, a number of new species descended from one species, that is a new genus, comes to supplant an old genus, belonging to the same family.
We may suppose that the numbered letters in italics represent genera, and the dotted lines diverging from them the species in each genus.
But in many other cases, in which we have reason to believe that the species of a genus have been produced within comparatively recent times, there is great difficulty on this head.
Expressions such as that famous one by Linnaeus, which we often meet with in a more or less concealed form, namely, that the characters do not make the genus, but that the genus gives the characters, seem to imply that some deeper bond is included in our classifications than mere resemblance.
The importance of an aggregate of characters, even when none are important, alone explains the aphorism enunciated by Linnaeus, namely, that the characters do not give the genus, but the genus gives the character; for this seems founded on the appreciation of many trifling points of resemblance, too slight to be defined.
Richard sagaciously saw, as Jussieu observes, that this genus should still be retained among the Malpighiaceae.
Nor can the existing species descended from A be ranked in the same genus with the parent A, or those from I with parent I.
But the existing genus F14 may be supposed to have been but slightly modified, and it will then rank with the parent genus F; just as some few still living organisms belong to Silurian genera.
All the descendants of the genus F, along its whole line of descent, are supposed to have been but little modified, and they form a single genus.
But this genus, though much isolated, will still occupy its proper intermediate position.
With respect to distinct species of the same genus, inhabiting distant and isolated regions, as the process of modification has necessarily been slow, all the means of migration will have been possible during a very long period; and consequently the difficulty of the wide diffusion of the species of the same genus is in some degree lessened.
For we have reason to believe that only a few species of a genus ever undergo change; the other species becoming utterly extinct and leaving no modified progeny.
How inexplicable on the theory of creation is the occasional appearance of stripes on the shoulders and legs of the several species of the horse-genus and of their hybrids!
Why, for instance, should the colour of a flower be more likely to vary in any one species of a genus, if the other species possess differently coloured flowers, than if all possessed the same coloured flowers?
This form of the common fresh-water CYCLOPS was described as a distinct genus under the name of NAUPLIUS.
The _avidum genus auricularum_, the gazing populace, receive greedily, without examination, whatever sooths superstition, and promotes wonder.
And thereby whalemen distinguish this fish from other tribes of his genus.
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