LECTURES ON BOTANY. 



233 



LECTURES ON BOTANY* 



COURSE OF LECTURES ON BOTANY IN REFERENCE TO AGRICULTURE. 



By Chart.es .Tohnsom, Esq., Profemtor of Botany at Gvy's Hospital, ^-c. ^-c. At Messrs. 

 Nesbits' AgricuUtiral and Scientific Training School, Kennington Lan^, Lambeth near 

 London. 



LECTURE III. leaves and stems of certain aquatic ve-^eta- 



The operations by which vegetable life bles, comparatively very low in the scafe of 

 and development or growth are maintained, being, flnids in consta)it motion, which, with 

 however plau.silily set forth by physiologists, iheir accompnnying phenomena, throw much 

 and perhaps con'ectly so in the aggregate, are light upon the process of increase iu the tis- 

 etill, in our present state of knowledge, for sue to which they belong 

 the most part incapable of po.sitive demon- 

 stration. Theii' combined effects ai'e seen in 

 the enlargement of parts previously formed 

 and the production of new ones. The leaf 

 opens from the bud, attains its destined size, 

 changes its hue, and falls ; the fi-uit ripens 

 and discharges its seed ; fhe seed gi'ows into 

 a plant, and the same processes are renewed 

 from year to year; but the organs that 

 minister to them are so minute, their mutual 

 action so complicated, tliat although the ex- 

 tem;J and grosser machinery of life is suffi- 

 ciently evident, the springs that work it are 

 involved in mystery. The microscope is too 

 limited iu its applicarion to effect much 

 toward the elucidation of the phenomena of 

 life. The child breaks his toy to find OTit the 

 source of the music wliich his act annihilates ; 

 and in like manner the philosopher tears up 

 the organic tissue, or at best deranges its 

 functions, that he may apply his glasses in 

 the vain effort to detect the origin of that 

 which is no longer there ; still something is 

 gained by both. The child has perhaps dis- 

 covered a strLnsr that produces a sound when 

 stntck, and a little wheel with spokes that 

 might have struck it ; while the philosopher 

 has discerned a few facts of wh-ich he was 

 previously ignorant ; and. in the end, each 

 of them " garring odds and evens meet," and 

 " laying that and that th'gither," find them- 

 selves a degi-ee wiser than before. The im- 

 portant fact of the circulation of the blood 

 was discovered and established by a similar 

 series of deductions ; and although its passage 

 from the arteries into the veins would be, 

 perhaps, vainly sought by inspection of die 

 miruite extremities of those of the higher an- 

 imals, in the translucent tail of a stickle-back, 

 or the membraneous foot of the frog, the di- 

 verging and returning cuiTcnts are beaulilidly 

 and obviously displayed. So in plants, al- 

 though the movements of the sap and other 

 juices cannot bo traced in the woody tubes 

 of the higher and more elaborately construct- 

 ed orders, yet the microscope discovers in 

 the cells of the minute and delicate hairs that 

 grow from their surface, and iu those of the 



In fig. 1 is represented the tenuination of 

 one of the slender, hair-like aquatic plants, 

 called " conferva? ; " which consists of litlla 

 transpai'ent cells, more or less elongated, and 

 joined end to end like a string of btvids. In 

 each of these cells the microscope discovers 

 currents of fluid, containing minute particles, 

 moving in the direction of the dotted lines, 

 and apparently circulating fiom on6 extremity 

 of the cell to the other, and returning on the 

 opposite side. In the center, or sometimes 

 toward one of the ends of the cell, is a small 

 cluster of particles, from and toward which 

 currents pass in a radiating manner, render- 

 ing tho combined movements very compli- 

 cated. The little central m:iss, however, evi- 

 dently greatly influences the rotation of tho 



' Contirnied from page 121, vol. iii. Monthly Journal of ATicultuie 

 (47:3) 



