SYSTEMATIC BOTANY. 



BOTANY is the science whose purpose it is to 

 investigate the Vegetable Kingdom. Vege- 

 table Physiology treated of in the preceding article 

 is that department of the subject which explains 

 the organisation and vital functions of plants ; 

 Systematic Botany, that which recognises their 

 arrangement into groups, according to their form 

 and structure. The former relates to functions 

 which are common to all vegetables ; the latter 

 takes notice only of such peculiarities as serve 

 to distinguish one species from another, or one 

 family from another family. The vegetable king- 

 dom is supposed to contain upwards of 150,000 

 species ; and therefore, without some system of 

 arrangement into smaller groups and orders, it 

 would be difficult to acquire a knowledge of the 

 special characteristics of plants, or to convey that 

 knowledge to others by any process of description. 

 It is the aim of Systematic Botany to obviate this 

 difficulty, by classifying plants according to certain 

 types and resemblances which are common to a 

 number of species ; thus making one description 

 equally applicable to a class as to a species. 



The advantages of classification in lessening 

 the labour of memory and description, become 

 strikingly apparent when we reflect on the diffi- 

 culty which would exist were each plant to be 

 known by an entirely distinct name. For example, 

 there are many species of roses, all of which are 

 known by the generic term Rosa, each having 

 a second or specific name to designate it separ- 

 ately, as Rosa canina (the dog-rose), &c. Now, if 

 a botanist hear of a plant called Rosa, though 

 its specific name be quite new to him, he has 

 instantly a general idea of what sort of plant 

 it is, from his previous knowledge of the common 

 characteristics which belong to the genus Rosa. 

 The principle of classification is to assemble those 

 plants which bear most resemblance to each 

 other ; and this has been done in different ways 

 by different botanists ; each method being called 

 the system of the individual who devised it as 

 Tournefort's system, Linnasus's system, Jussieu's 

 system. Of the several systems which have been 

 suggested, only two are in use at the present time 

 namely, that of Linnasus, the great Swedish 

 naturalist (1707-1778) ; and the Natural System, 

 in its numerous modifications, that of Jussieu, an 

 eminent French botanist, who, during the long 

 period between 1789 and 1836, was closely engaged 

 in improving the nomenclature and arrangement 

 of the vegetable kingdom, having afforded the 

 basis of those mostly in use. 



The system of Linnaeus is founded on the sexes 

 in plants the number, situation, proportion, and 

 connection of stamens and pistils, which are 

 regarded as respectively the male and female 

 organs, being chosen to supply characters for the 

 classes and orders. This system appears at first 

 sight extremely simple, as it depends entirely on 

 the counting of so many visible parts ; but it is 

 very uncertain, as the number of stamens often 

 differs, from accidental circumstances, in plants of 

 the same genus ; and it tells nothing of the plant 

 but its class and order, which lead only to the 

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discovery of its technical name, as plants of the 

 most opposite qualities frequently agree in the 

 number and disposal of their sexual organs. This 

 mode of classification is known among botanists 

 as the Sexual System, or the Artificial System, 

 because it is founded on mere artificial enumer- 

 ation, on a single series of characters, and not 

 upon natural qualities or resemblances of the 

 plants so arranged. That of Jussieu, on the 

 contrary, is founded on the natural affinities ; and 

 the botanist who is acquainted with its principles 

 can at first sight assign any plant to its proper 

 class and order, as there is always a general 

 resemblance among the plants belonging to the 

 same natural order. Again, knowing the order, 

 which is usually typified by some common plant, 

 he can predict as to its properties a species of 

 information which the artificial system does not 

 attempt to convey. Jussieu's method has been 

 greatly improved since the time it was suggested, 

 particularly by the late Professor De Candolle of 

 Geneva ; and it is his modification of the original 

 plan, with further improvements, which constitutes 

 the most generally adopted Natural System of the 

 present day. 



According to both systems, plants are divided 

 into classes, orders, genera, species, and varieties. 

 A class consists of plants resembling each other 

 in some grand leading feature, and as strongly 

 differing from another class as mammalia do from 

 birds, for example. Thus, flowering-plants with 

 one cotyledon (or seed-lobe), whose trunks increase 

 in thickness from within as the palm form a 

 distinct class ; while flowering-plants with two 

 cotyledons, and whose trunks increase by external 

 layers, constitute another class. An order consists 

 of plants still more closely allied, so that many 

 orders may be found in the same class. Thus, as 

 ruminant or cud-chewing animals form an order 

 of mammalia, so do the leguminous or pod-bearing 

 plants constitute an order of dicotyledonous vege- 

 tation. A genus consists of plants so very closely 

 allied, that they may be compared to members 

 of the same family. The pea, for example, con- 

 stitutes a genus of leguminous plants, just as sheep 

 form a family of the ruminants. A species may 

 be compared to one of the members which com- 

 pose the family ; thus the garden-pea and sweet- 

 pea are different species of the same genus. A 

 variety is merely a departure from the common 

 appearance of the species in trivial characters, or 

 differences which arise from climate, situation, 

 greater or less humidity of soil, and other acci- 

 dental causes. The boundaries between species 

 and varieties are often very vague, some botanists 

 regarding those plants as species which others 

 consider mere varieties ; but much doubt might 

 be removed by attending to the fact, that a species 

 reproduces itself from seed, and is always per- 

 sistent under the same circumstances, whereas a 

 variety has often a tendency to revert to its parent 

 species, unless propagated by cuttings, and fos- 

 tered by artificial means. A hybrid is a plant 

 raised by fecundating the stigma of one species 

 with the pollen of another a process which 



