32 rNTBODTJCTION. 



Shade, on the contrary, especially if accompanied by richness of soil and 

 BufBcient moisture, tends to increase the foliage and draw up the stem, but 

 to diminish the number, size, and colour of the flowers. 



A liot climate and dry situation tend to increase the hairs, prickles, and 

 other productions of the epidermis, to shorten and stitien the branches, 

 rendering thorny plants yet more spinous. Moisture in a rich soil has a 

 contrary effect. 



The neighbourhood of the sea, or a saline soil or atmosphere, imparts a 

 thicker and more succulent consistence to the foliage and almost every part 

 of the (ilant, and appears not unfrequently to enable plants usually annual 

 to live through the winter. Flowers in a maritime variety are often much 

 fewer, but not smaller. 



The luxuriance of plants growing isolated 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 spe- 

 cimens of a species become dwarf and stunted as we advance into the cold 

 damp regions of the summits of liigh mountain ranges, or into high northern 

 latitudes ; and yet it is very frequently from the want of attention to these 

 circumstances that numbers ot false species have been added to our Enume- 

 rations and Floras. Luxuriance entails not only increase of size of the 

 whole plant, or of particular parts, but increase of number in branches, or 

 leaves, or leaflets of a compound leaf; or it may diminish the hairiness of 

 the plant, or induce thorns to grow out into branches, etc. 



Capsules which, whde growing, he upon or close to the ground, will often 

 becoine larger, more succulent, and less readily dehiscent than those which 

 are not so exposed to the moisture of the soU. 



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 axid climate, will send up luxu- 

 riant side-shoots, often so diflerent in the form of their leaves, in their ra- 

 mification 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 diflerent in aspect from individuals of the same species, 

 which, having germinated later, are stopped by summer di-oughts or the 

 approach of winter, and only flower the following season upon a second 

 growth. The latter have often been mis aken for perennials. 



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 subject there is much diversity in 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 loild hyhrid. 



It partakes of the characters of its two parents. 



It is to be found isolated, or almost 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.. 



Whei'e two supposed species grow together, intermixed with uumeroua 



