LECTURES ON BOTANY. 



115 



LECTURES ON BOTANY* 



COURSE OF LECTURES ON BOTANY IN REFERENCE TO AGRICULTURE. 

 By Charles Johnson, Esq,, Professor of Botany at Guy's Hospital, i^-r. i^-c. At Messrs. 

 Nesbit's Agricultural and Scientific Training School, Kennington Lane, Lambeth, near 

 London. 



LECTURE II. 



Our preceding Lectiu-e was dedicated to 

 the detail of a few of the advantages that liave 

 aheady residted from the knowledge of a 

 simple fact in vegetable physiology, namely, 

 the influence of the external organs or parts 

 of the flower in the production of the seed. 

 It is a subject on which we might dwell at 

 much greater length, as manifesting the vast 

 importance of a branch of study that the 

 practical cultivator, regarding it generally in 

 the light of an abstract science, has hitherto 

 considered rather as an amusement for the 

 idle speculator, than as intimately comiecled 

 with the practice of his profession, and illus- 

 trating those processes of his art that have 

 been established by the slowly accmiiulated 

 experience of himself and liis predecessors. 

 But this early stage of our inquiry is not the 

 fitting place to extend our remarks upon the 

 action of organs whose operation can scarcely 

 be comprehended without reference to their 

 own ultimate structure — in other words, to 

 the minute organs or vessels of which diey 

 ai'e themselves built up; andtliis observation 

 applies not only to the flower, but to every 

 part of the vegetable fabric : every product 

 of the plant, whether cultivated for food or 

 as adapted to the other almost innumerable 

 wants and purposes of man — nay, its very 

 existence — is dependent upon these. 



A vegetiible is a living being, and, as such, 

 is made up of parts or members, all more or 

 less influencing each other, and united and 

 simultiuieous iu their oi)erations for the 

 growth and preservation of the whole. Some 

 parts, wlien cut through, appear solid to the 

 naked eye, others present a minutely jiorous 

 appearance ; l)ut under a microscope or strong 

 magnifying-glass the apparent solidity of the 

 hardest and closest wood disapp(;afs. It is 

 in these small and all but invisil)le cavities 

 that the vital functions of the being before us 

 are to be traced ; it is here that are elaborated 

 the starch, the gluten, the guni, the sugar, and 

 the other jiroximate principles of our food ; 

 here are formed the Uuuiin. the dye, the 

 medicine ; the production of the wood, the 

 balk, the diflering flbre of the flax luid cot- 

 ton, and the increase of the universiJ sub- 

 stance of the plant itself, are all of them pro- 

 cesses depeiuicnt U[)on the economy of these 

 mysterious recesses. The piying eye of cu- 

 riosity is sometimes at fault in its endeavors 

 to penetrate the sources of orgardc action, but 

 a glance is often sullicient for the speculative 



mind of man to work upon and form a hy- 

 pothesis which a second wll enable him to 

 improve into a theoiy, and although we posi- 

 tively know but little, that little enables us 

 to assume a great deal, and this is especially 

 the case as regards the science of Vegetable 

 Physiology, or tliat which treats of the nat- 

 ural laws regulating the growth of i)lantsand 

 their productions,, as just referred to. Iu 

 giving you a general outline of the action of 

 these laws, and endeavoring to explain the 

 structure through which they operate, I shall 

 avoid as much as possible reference to what 

 is merely supposititious, relying upon the 

 statement of facts, and such conclusions as, 

 though in our present state of knowledge 

 they are incapable ofbemg positively demon- 

 strated, are still so closelj' accordant with 

 what we really do know, tliat, until they are 

 contradicted by facts, we are justified in re- 

 garding them as such themselves. 



Divide the stem of any common plant 

 transversely or crosswise, and examine the 

 section with a microscope, it will present the 

 appearance of net- work, the meshes of which 

 are of various sizes and tigures, some perhaps 

 regularly hexagonal, or six-sided, like the cells 

 of a honey-comb, others more irregular, oth- 

 ers square, and some circular ; the circular 

 ones are generally disposed in gi-oups; which 

 are sometimes scattered, sometimes arranged 

 at corresponding intervals in a concentric 

 manner. If we divide the same stem per- 

 pendicularly, or lengthwise, we find the an- 

 gular meshes presenting a nearly siniilai- aj)- 

 pearance, shovving them to be small, mem- 

 braneous cells or cavities, while the circular 

 ones are discovered to be sections of littlo 

 tubes, more or less elongated, anil narrowing 

 toward each extremity so as to teruiinate iu 

 a point, and farther that they arc dis])osed in 

 longitudinal layers, or thread-like bundles. 

 These cells and tubes are deiiominateil the 

 elemenfcuy organs of the plant ; and minute 

 examinaiion of them shows that, independent 

 of dirterences in form, size, and disposition, 

 ihey vary greatly in structure, and are prob- 

 ably subservient, in consequence of that va- 

 riation, to the perlbnnance of different fimc- 

 tions ; these functions, liowevei', are, in our 

 present sUite of knowledge, very iinj)erfectly 

 understood ; of many, and those perhaps the 

 most important, wo are altogether ignorant ; 

 while otiiers are little more than surmised, 

 from their apparent connection with some 

 obvious fact in vegetable gi-owth, such as the 



Continued from page 377, Vol. II., Monthly Journal of Agriculture. 

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