DEVELOPMENT OF CELLS. 15 



Bacterium, etc. The doctrine of biogenesis (j8/oc, life), panspermism 

 {■^av, all, g-jrii/idj seed), or the development of cells in fluid from germs 

 introduced from the atmosphere, has been advocated by Pasteur and 

 his followers ; while the doctrine of abiogenesis (a, privative, and j3log, 

 life), heterogenesis (sVejos, different, diverse), or what is called spon- 

 taneous generation, has been supported by Pouchet and his followers. 

 All that is known in regard to the growth of the lower class of plants, 

 and their appearance in islands recently elevated by volcanic forces in 

 the midst of the ocean, seems, independently of laboratory experi- 

 ments, to favour Pasteur's views.* 



The organised cells of plants appear to be the more immediate seats 

 of the various changes which constitute the functions of nutrition and 

 teproduction. In cellular plants they are the only form of elementary 

 tissue produced throughout the whole of life. They absorb nourish- 

 ment through their walls, elaborate secretions, and give rise to new 

 individuals. In the newly-formed tissue of vascular plants, cells 

 alone at first exist, fluid matters are absorbed by them, and are 

 transmitted from cell to cell by a process of transudation. The 

 name of Endosmose (ev3ov, inwards, fidu, ^S, I seek), and Exosmose 

 (eJw, outwards), were given by Dutrochet to the process of transuda- 

 tion, which leads to the motions of fluids of difierent densities placed 

 on opposite sides of animal and vegetable membranes. This process 

 appears to be of universal occurrence in plants, being concerned in 

 the movements of the sap, the opening of seed-vessels, and many 

 other phenomena. The capsule of the Elaterium, for instance, opens 

 with great force by a process of endosmose going on in the cells, and 

 such is also the case with that of the Balsam. The power which 

 cells possess of absorbing fluids is well seen in sea-weeds, which after 

 being dried can easily be made to assume their natural appearance 

 by immersion in fluids. It is also observable in the spores of the 

 Equisetum, the teeth of Mosses, the seed-vessels of some Fig-mari- 

 golds, the Eose of Jericho (Anastatica), and some Lycopodia. 



Various organic secretions, which are necessary for growth and 

 nourishment, are formed by the internal membrane of cells. It is in 

 cells that the azotised and unazotised matters are deposited, which 

 are afterwards applied to the purposes of vegetable life. In them 

 we meet with the protein compounds, albumin, fibrin, and casein, 

 consisting of carbon, oxygen, hydrogen, and nitrogen, with proportions 

 of sulphur and phosphorus ; as well as starch, gum, sugar, oil, and 

 colouring matters, in which no nitrogen occurs. Some of the organic 

 matters found in plants have been artificially formed by chemical 

 means, while others have as yet only been met with in the living 

 organism. Spiral cells sometimes contain air. 



* See Professor Lister on Bacteria, in Medical Jmirnal, October 1873 ; and Dr. Petti- 

 grew's Lecture on Physiology, in Lantxt, 15th November 1873. 



