204 



'^ KNOWLEDGE ♦ 



[May 1, 1886. 



although green plants, under the action of light, break np 

 carbonic acid and release the oxygen, tliey do the reverse in 

 the dark, as also in respiration ; while the quasi-animal 

 fungi, which are independent of light, absorb oxygen and 

 give off carbonic acid. 



In the " irritability " of the sundew, Yenus's fly-trap, and 

 other sensitive phxnts, still more so in subtile and hidden 

 movements in plant-cells, we have actions corresponding to 

 those called "reflex" in animals, as the contraction of the 

 shapeless amoiba when touched, or the involuntary closing 

 of our eyelid when the eye is threatened, or the drawing 

 back of one's .feet when tickled. The filament in the 

 amoiba which transmits the impulse causing it to contract 

 difters only in degres from the sensory nerves in ourselves 

 which transmit the impression to the motor nerves, causing 

 the muscles to act; and since there is every reason for 

 referring tlie contractile action of plants, i.e. their movements 

 in obedience to stimulus, to like causes, the germs of a 

 nervous system must be conceded to them. The minute 

 obsarvations of Mr. Darwin and his son into the large class 

 of quasi-animal movements common to wellnigh all vege- 

 table life go far to condrm this. The highly sensitive tip of 

 the slowly revolving root, in directing the movements of the 

 adjoining parts, transmitting sensation from cell to cell, 

 " acts like the brain of one of the lower animals ; the brain 

 being seated within the anterior end of the body, receiving 

 impressions from the sense organs and directing the several 

 movements." 



In these and kindred vital processes, in the so-called sleep 

 of leaves, and the opening and closing of flowers, both regu- 

 lated by the amount of light, apparently acting on them as 

 it acts on our nervous system ; in the detection of subtle 

 differences in light, which escape the human eye, by plants: in 

 their general .sensitiveness to external influences, even in the 

 diseases which attack them, the study of which Sir James 

 Paget has commended to pathologists, we have the rudiments 

 of attributes and powers which reach their full development 

 in the higher animals, and therefore a series of funda- 

 mental correspondences between plant and animal whicli 

 point to the merging of their apparent diflerences in one 

 community of origin. 



In fine, that which was once thought special to one is 

 found to be common to both, and to this there is no excep- 

 tion. Not only is there correspondence in external form in 

 the lower life-groups, but, fundamentally, plants and animals 

 are alike in internal structure, and in the discharge of the 

 mysterious processes of nutrition (although, as will be shown 

 presently, this forms a convenient line of separation) and 

 of reproduction. All, from the lowest to the highest, have 

 their unity and kinship in ancestral life which was neither 

 plant nor animal. 



Of course the difEculty of classifying vani.shes in tlie 

 higher forms ; the lowest plants are allied to the lowest 

 animals, but the higher the plant the more it diverges from 

 the animal, which is evidence that in the succession of life 

 the highest plants do not pass into the lower animals. 

 Descent is not lineal, but lateral ; the relations between the 

 two kingdoms are represented by two lines starting from a 

 common point and spreading in diS'erent directions. Even 

 " lower" and " higher " are relative terms; the organisation 

 of the amceba is as complete for its purpose as is that of the 

 man for his i)iu'pose, the modification in the complex forms 

 being due to the division of functions which are j)erformed 

 in every part by the simple forms. 



Although the foreg^iing and numberless other facts, 

 together with the law of continuity, alike forbid the drawing 

 of any hard and fast lines, and involve the conclusion, to 

 borrow Professor Huxley's words, " that the difference 

 between animal and plant is o.ie of degree rather than of 



kind, and that the problem whether in a given case an 

 organism is an animal or a plant may be es.sentially in- 

 soluble," there exists, exceptions notwithstanding, a broad 

 distinction in the mode of nutrition. 



" All things the world which fill 

 0£ but one stuff are spun," 



and this stufl' the basis of all life, the formative power, is a 

 semi-fluid, sticky material, full of numberless minute granules 

 in ceaseless and rapid motion, to which the name " proto- 

 plasm " (Gr. pfutos, first ; plasma, formed) has been given, 

 it consists of four of the elementaiy substances, carbon, 

 hydrogen, oxygen, and nitrogen, complexly united in the 

 compound called protein, whiclr is closely identical with the 

 albumen or white of an egg. These are the essential 

 elements, but a few others enter iuto the chemistry of life, 

 with slight resulting differences in the incidental elements 

 ia animals and plants. As water is necessar}' to all vital 

 processes, a very large proportion enters into living matter. 

 But there is this fundamental and significant difference 

 between the two kingdoms. The plant posse.sses the myste- 

 rious ])ower of weaving the visible out of the invisible ; of 

 converting the lifeless into the living. This it does in 

 virtue of the chlorophyll, or green colouring matter, which 

 is found united with definite portions of the protjplasm- 

 mass, of whicli it is a modification, the exact nature being 

 unknown.* The water and carbonic acid which the plaut 

 absorbs through the numbei-less stomata or mouth-pores in 

 its leaves or integument are, when the sunlight falls upon 

 them, broken up by the chlorojjhylljt which sets free the 

 oxygen, and locks together the hydrogen and carbon, con- 

 verting this hydro-carbon into the simple and complex cells 

 and tissues of the plant, with their store of energy for service 

 to it.self and other organisms. Animals, a few low forms ex- 

 cepted, cannot do this ; they are powerless to convert water, 

 salts, gases, or any other inorganic substances, into organic ; 

 they are able only to assimilate the matter thus supplied by 

 the plant, nourishing themselves therewith either directly, 

 by eating the plant, or indirectly, by eating some jilant- 

 feeding animal. In other words, the plant manufactures 

 protein fiom the mineral world, and the animal obtains 

 the protein ready-made ; the plant converts the simple into 

 the complex; and this the animal, by combining it with 

 oxygen, consumes, using u]j the energy it thei-eby obtains in 

 doing work. So the plant is the origin of all the energy 

 possessed by living things, but why it can by virtue of the 

 sunshine convert the stable inorganic into the unstable 

 organic, while tlie animal cannot, we do not know. Neither 

 do we know whether plant preceded animal, or vice versa, 

 in life's beginnings, although the evidence, which will be 

 considered in its place, seems to point in favour of the 

 priority of the plant. Structurally the lowest animal is 

 below the lowest plant, since it is a speck of formless 

 colourless protoplasm, whereas the ])roto]ilasm of the lowest 

 plant is organised to the extent that it has formed for itself 

 an outer layer or membranous coat called the cell-wall. 

 For example, the ^-egetablo character of yeast-gi-anulcs 

 is determined, apart from their mode of nutrition, by the 

 protoplasm being inclosed within a cellulose coat, and the 

 animal character of the amosba, not because of contractile or 

 locomotive pjwer or of inability to manufacture protein 

 from inorganic matter, but by the abssnce of any such 

 covering. Upon this Haeckel remarks that the vegetable 

 cells sealed their fate when inclosed within a hard thick 

 cellular shell, being thereby less accessible to external influ- 



* Chlorophyll is found in green fresh- water polyps and a few other 

 small animals, but is thougbl to be due to a vegetable parasite. 



t The formation of chlorophyll in complete darkness, but under 

 sufficiently high temperature, has been obserfed in a few Instances. 



