388 



NATURE 



\August 21, 1879 



t 



In the several instances now adduced the protoplasm is in the 

 mature state of the plant entirely included within a wall of cellu- 

 lose. Some recent beautiful observations, however, of Mr. 

 Francis Darwin have shown that even in the higher plants truly 

 naked protoplasm may occur. From the cells of certain glan- 

 dular hairs contained within the cup-like receptacles formed by 

 the united bases of two opposite leaves in the Teazel (DiJ>sacus) 

 he has seen emitted long pseudopodia-like projections of the 

 protoplasm. What may be the significance of this very excep- 

 tional phenomenon is still undetermined. It is probably as Mr. 

 Darwin suppo;es connected with the absorption of nitrogenous 

 matter. 



That there is no'essential difference between the protoplasm 

 of plants and that of animals is rendered further evident by 

 other motor phenomena, which we are in the habit of regarding 

 as the exclusive attribute of animals. Many of the more simply 

 organised plants give origin to peculiar cells called spores, which 

 separate from the parent, and, like the seeds of the higher plants, 

 are destined to repeat its form. In many cases these spores are 

 eminently locomotive. They are then termed "swarm spores," 

 and their movements are brought about, sometimes by changes of 

 shape, when they move about in the manner of an Amtxba, but 

 more frequently by minute vibratile cilia, or by more strongly 

 developed flagella or whip-like projections of their protoplasm. 

 These cilia and flagella are absolutely indistinguishable from 

 similar structures vddely distributed among animals, and by 

 their vibratory or lashing strokes upon the surrounding water 

 the swarm-spores are rapidly carried from place to place. In 

 these motions they often present a curious semblance of volition, 

 for if the swarm-spore meet with an obstacle in its course, it 

 \vill, as if to avoid it, change the direction of its motion, and 

 retreat by a reversion of the stroke of its cilia. They are usually 

 attracted by light, and congregate at the light side of the vessel 

 which contains them, though in some cases light has the opposite 

 effect on them, and they recede from it. 



Another fact may here be adduced to show the uniform cha- 

 racter of protoplasm and how very different are its properties 

 from those of lifeless matter, namely, the faculty which all 

 living protoplasm possesses of resisting the entrance of colouring 

 matter into its substance. As many here present are aware, 

 micro-copists are in the habit of using in their investigations 

 various colouring matters, such as solutions of carmine. These 

 act differently on the different tissues, staining some, for ex- 

 ample, more deeply than others, and thus enabling the histolo- 

 gist to detect certain elements of structure, which would other- 

 wise remain unknown. Now if a solution of carmine be 

 brought into contact with living protoplasm, this will remain, 

 so long as it continues alive, unaffected by the colouring matter. 

 But if the protoplasm be killed, the carmine will at once pervade 

 its whole substance, and stain it throughout with a colour more 

 intense than even that of the colouring solution itself. 



But no more illustrative example can be offered of the proper- 

 ties of protoplasm as living matter, independently of any part 

 it may take in organisation, than that presented by the Myxo- 

 jnycetse. 



The Myxcmyceta: constitute a group of remarkable organisms, 

 which, from their comparatively large size and their consisting, 

 during a great part of their lives, of naked protoplasm, have 

 afforded a fine field for research, and have become one of the 

 chief sources from which our knowledge of the nature and phe- 

 nomena of protoplasm has been derived. 



They have generally been associated by botanists with the 

 fungi, but though their affinities with these are perhaps closer 

 than with any other plants, they differ from them in so many 

 points, especially in their development, as to render this associa- 

 tion untenable. They are found in moist situations, growing on 

 old tan or on mo.s, or decaying leaves or rotten wood, over 

 which they spread in the form of a network of naked protoplas- 

 mic filaments, of a soft creamy consistence, and usually of a 

 yellowish colour. 



Under the microscope the filaments of the network exhibit 

 active spontaneous movements, which, in the larger branches, 

 are vi>ible under an ordinary lens, or even by the naked eye. A 

 succession of undulations may then be noticed passing along the 

 course of the threads. Under higher magnifying powers a con- 

 stant movement of granules may be seen flowing along the 

 threads, and streaming from branch to branch cf this wonderful 

 network. Here and there off-hoots of the protopla-m are pro- 

 jected, and again withdrawn in the manner of the p eudopodia 

 of an Aiiiixba, while the whole organism may be occasionally 



seen to abandon the support over which it had grown, and to 

 creep over neighbouring surfaces, thus far resembling in all 

 respects a colossal ramified Amccba. It is also curiously sensi- 

 tive to light, and may be sometimes found to have retreated 

 during the day to the dark side of the leaves, or into the recesses 

 of the tan over which it had been growing, and again to creep 

 out on the approach of night. 



After a time there arise from the surface of this protoplasmic 

 net oval capsules or spore cases, in which are contained the 

 spores or reproductive bodies of the MyxomycetEe. When the 

 spore-case has arrived at maturity, it bursts and allows the spores 

 to escape. These are in the form of sjiherical cells, each 

 included in a delicate membranous wall, and when they fall into 

 water the wall becomes ruptured, and the little cell creeps out. 

 This consists of a little mass of protoplasm with a round central 

 nucleus, inclosing a nucleolus, and with a clear vacuole, which 

 exhibits a rhythmically pulsating movement. The little naked 

 spore thus set at liberty is soon seen to be drawn out at one 

 point into a long vibratile whip-like flagellum, which by its 

 lashing action carries the spore from place to place. After a 

 time the flagellum disappears, and the spore may now be seen 

 emitting and withdrawing finger-like pseudopodia, by means of 

 which it creeps about like zn Amceba, andlike an ^;«tt'iJa devours 

 solid particles by engulfing them in its soft protopla.sm. 



So far these young Amaba-Wke Myxomycetre have enjoyed 

 each an independent existence. Now, however, a singular and 

 significant phenomenon is presented. Two or more of these 

 Myxamoeba;, as they have been called, approach one another, 

 come into contact, and finally become completely fused together 

 into a single mass of protoplasm, in which the components are 

 no longer to be distinguished. To the body thus formed by the 

 fusion of the Myxamoeba; the name of " Plasmodium" has been 

 given. 



The Plasmodium continues, like the simple amcebiform bodies 

 of which it is composed, to grow by the ingestion and assimila- 

 tion of solid nutriment, which it envelopes in its substance ; it 

 throws out ramifying and mosculating processes, and finally 

 becomes converted into a protoplasmic network, which in its 

 turn gives rise to spore-cases with their contained spores, and 

 thus completes the cycle of its development. 



Under certain external conditions, the Myxomyceta; have heeu 

 observed to pass from an active mobile state into a resting state, 

 aird this may occur both in the amcebiform spores and in the Plas- 

 modium. When the plasmodiura is about to pass into a resting 

 stale, it usually withdraw s its finer branches, and expels such solid 

 ingesta as may be included in it. Its motions then gradually 

 cease, it breaks up into a multitude of polyhedral cells, which, 

 however, remain connected, and the whole body dries into a 

 horny brittle mass, known by the name of " sclerotium." 



In this condition, without giving the slightest sign of life, the 

 sclerotium may remain for many months. Life, however, is not 

 destroyed, its manifestations are only suspended, and if after an 

 indefinite time the apparently dead sclerotium be placed in water, 

 it immediately begins to swell up, the membranous covering of 

 its component cells becomes dissolved and disappears, and 

 the cells themselves flow together into an active amoeboid 

 Plasmodium. 



We have already seen that every cell posseses an autonomy or 

 independent individuality, and from this we should expect that, 

 lilve all living beings it had the faculty of multiplying itself, and 

 of becoming the parent of other cells. This is truly the ca^e, 

 and the process of cell-multiplication has of late years been 

 studied, w ith the re.=ult of adding largely to our knowledge of 

 the phenomena of life. 



The labours of Strasburger, of Auerbach, of Oscar Hertwig, 

 of Eduard van Beneden, Biitschli, Fol, and others, here come 

 prominently before us, but neither the time at my disposal nor 

 the purport of this address will allow me to do more than call 

 your attention to some of the more striking results of their 

 investigations. 



By far the most frequent mode of multiplication among cells 

 shows itself in a spontaneous division of the protoplasm into 

 two separate portions, which then become independent of one 

 another, so that instead of the single parent cell two new ones 

 have made their appearance. In this process the nucleus usually 

 takes an important part. Strasburger has studied it with great 

 care in certain plant cells, such as the so-called "corpuscula" 

 or "secondary embryo- sacs" of the Conifera; and the cells of 

 Spirogyra ; and has further shown a close correspondence between 

 cell division in animals and that in plants. 



