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INTRODUCTION. XXXV11 



ars not unfrequently to enable plants usually annual to live through the winter, 

 lowers in a maritime variety are often much fewer, but not smaller. 



The luxuriance of plants growing in a rich soil, and the dwarf stunted character of 

 those crowded in poor soils, are too well known to need particularizing. It is also an 

 everyday observation how gradually the specimens of a species become dwarf and 

 stunted as we advance into the cold damp regions of the summits of high mountain 

 ranges, or into high northern latitudes ; and yet it is frequently from the want of at- 

 tention to these circumstances that numbers of false species have been added to our 

 Enumerations and Floras. Luxuriance entails not only increase of size to the whole 

 plant, or of particular parts, but increase of number in branches, in leaves, or leaflets 

 of a compound leaf ; or it may diminish the hairiness of the plant, induce thorns to 

 grow out into branches, etc. 



Capsules which, while growing, lie close upon the ground, will often become larger, 

 more succulent, and less readily dehiscent, than those which are not so exposed to the 

 moisture of the soil. 



Herbs eaten down by sheep or cattle, or crushed underfoot, or otherwise checked in 

 their growth, or trees or shrubs cut down to the ground, if then exposed to favourable 

 circumstances of soil and climate, will send up luxuriant side-shoots, often so different 

 in the form of their leaves, in their ramification and inflorescence, as to be scarcely re- 

 cognizable for the same species. 



Annuals which have germinated in spring, and flowered without check, will often be 

 very different in aspect from individuals of the same species, which, having germinated 

 later, are stopped by summer droughts or the approach of winter, and only flower the 

 following season upon a second growth. The latter have often been mistaken for per- 

 ennials. 



Hybrids, or crosses between two distinct species, come under the same category of 

 anomalous specimens from a known cause. Frequent as they are in gardens, where 

 they are artificially produced, they are probably rare in nature, although on this sub- 

 ject there is much diversity of opinion, some believing them to be very frequent, others 

 almost denying their existence. Absolute proof of the origin of a plant found wild, is 

 of course impossible ; but it is pretty generally agreed that the following particulars 

 must always co-exist in a wild hybrid. It partakes of the characters of its two parents j 

 it is to be found isolated, or almost isolated, in places where the two parents are abun- 

 dant ; it there are two or three, they will generally be dissimilar from each other, one 

 partaking more of one parent, another of the other ; it seldom ripens good seed j it will 

 never be found where one of the parents grows alone. 



Where two supposed species grow together, intermixed with numerous intermediates 

 bearing good seed, and passing more or less gradually from the one to the other, it 

 may generally be concluded that the whole are mere varieties of one species. The be- 

 ginner, however, must be very cautious not to set down a specimen as intermediate 

 between two species, because it appears to be so hi some, even the most striking cha- 

 racters, such as stature and foliage. Extreme varieties of one species are connected 

 together by transitions in all their characters, but these transitions are not all observa- 

 ble in the same specimens. The observation of a single intermediate is therefore of 

 little value, unless it be one link in a long series of intermediate forms, and, when met 

 with, should lead to the search for the other connecting links. 



2. Accidental aberrations from the ordinary type, that is, those of which the cause 

 is unknown. 



These require the more attention, as they may sometimes lead the beginner far astray 

 in his search for the genus, whilst the aberrations above-mentioned as reducible more or 

 less to general laws, affect chiefly the distinction of species. 



Almost all species with coloured flowers are liable to occur occasionally with them 

 all white. 



Many may be found even in a wild state with double flowers, that is, with a multi- 

 plication of petals. 



Plants Which have usually conspicuous petals will occasionally appear without any 

 at all, either to the flowers produced at particular seasons, or to all the flowers of in- 

 dividual plants, or the petals may be reduced to narrow slips. 



