1 INTRODUCTION. 



through the winter. Flowers in a maritime variety are often much fewer, but 

 not smaller. 



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

 racter 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 be- 

 come dwarf and stunted as we advance into the cold damp regions of the sum- 

 mits of high mountain-ranges, or into high northern latitudes ; and yet it is 

 frequently from the want of attention 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, w T hile 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 ex- 

 posed 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 recognizable 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 perennials. 



Hybrids, or crosses between two distinct species, come under the same cate- 

 gory of anomalous specimensfrom a known cause. Frcquentas they are in gardens, 

 where they are artificially produced, they are probably rare in nature, although 

 on this subject 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 ivild hybrid. It 

 partakes of the characters of its two parents ; it is to be found isolated, or al- 

 most isolated, in places where the two parents are abundant ; if 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 ; it will never 

 be found where one of the parents grows alone. 



Where two supposed species grow together, intermixed with numerous in- 

 termediates 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 beginner, however, must be very cautious not to set down a 

 specimen as intermediate between two species, because it appears to be so in 

 some, even the most striking characters, such as stature and foliage. Extreme 

 varieties of one species are connected together by transitions in all their cha- 

 racters, but these transitions are not all observable 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 ivhicli 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. 



