354 



SCIENCE. 



[Vol. XIV. No. 355 



Rodewald and Reinke on a large scale, by Loew and Bokorny, and 

 by Schwarz under the microscope. All of these results compel us 

 to recognize in protoplasm a substance of bewildering complexity 

 of composition and constitution. Moreover, you all know how 

 wide this field of research has suddenly become by the discovery 

 that different microbes (which are essentially minutest masses of 

 protoplasm) not only give rise to such diverse products, among 

 others the ptomaines, but present such diverse chemical re-ac- 

 tions. 



Protoplasm is no longer regarded by any one in any sense as a 

 comparatively simple substance. 



The third thesis, namely, protoplasm has no demonstrable struc- 

 ture, has been modified in a striking manner as a result of im- 

 proved appliances for research. By better methods of staining, and 

 by the use of homogeneous immersion objectives, the apparently 

 structureless mass is seen to be made up of parts which are easily 

 distinguishable. There has been, and in fact is now, a suspicion 

 that some of these appearances, under the influence of staining- 

 agents, are post-mortem changes, and do not belong to protoplasm 

 in a living state. But it seems to be beyond reasonable doubt that 

 protoplasm is marvellously complex in its morphological and physi- 

 cal as well as its chemical constitution. One statement of the case 

 is as follows : Under ordinary circumstances, protoplasm is com- 

 posed of a mesh of inconceivable fineness, in'which mesh are en- 

 tangled the more liquid interfilar portions (paraplasnia) ; so that 

 the dry husks left in Reinke's experiment may be regarded as the 

 residue of network from which all the moisture has been expelled. 

 But this conception of protoplasm as a mass composed of a net- 

 work of minutest fibres enclosing in the meshes another substance, 

 presents, as has been well shown by some critics, great difficulties 

 when we endeavor to explain the movements within the cell. It 

 is very difficult to explain in any way the so-called wandering of 

 protoplasm outside the cell wall or into intercellular spaces. 



Fourth, we are to glance at the accepted statement that the 

 protoplasmic body or protoplast, as it is called, of one cell is cut 

 off by the cell wall from all connection with the contiguous cells. 

 There are a few cases in which this intervening wall was formerly 

 held to be pervious, but such cases were considered as exceptional. 

 Now, however, as has been shown by Gardiner and others who 

 have followed out his exact researches, there are intercommunicat- 

 ing threads of protoplasm of extreme fineness between adjoining 

 cells ; and these living threads maintain connections, sometimes 

 direct, sometimes indirect, between one protoplasmic mass and 

 another. This has been shown to be so widely true in the case of 

 the plants hitherto investigated, that the generalization has been 

 ventured on, that all the protoplasm throughout the plant is con- 

 tinuous. The formation of the dividing wall in cell-division is now 

 better understood than ever before, and our knowledge of this pro- 

 cess lends great probability to the truth of the general statement 

 made. It is not unlikely, then, that all the living matter through- 

 out each plant is continuous, a whole, shut off at the time of sever- 

 ing from the mother-plant from the body of protoplasm there, and 

 thus making a true chain of descent. 



May I ask you to observe, in passing, how this bears on the 

 vexed subject of individuality of plants.' Briicke, in 1862, de- 

 clared that the living protoplasmic contents of a cell formed an 

 elementary organism, and this idea found its fullest expression in 

 the profound work by Hanstein in 1880. In that treatise Hanstein 

 proposed for the living protoplasmic contents of the cell the term 

 " protoplast," in order to indicate its individuality. But these late 

 researches show that these protoplasts are not only highly organ- 

 ized and of complicated structure, but each is bound by indissolu- 

 ble ties to its nearest neighbors, each helping to form a united 

 whole. 



The fifth thesis has been completely controverted. Instead of 

 believing, as formerly, that all the granules within the cell arise de 

 Jicmo from the protoplasm in which they are embedded, we are now 

 forced to regard all of them as springing from pre-existent bodies 

 of the same character. 



Hofmeister, in 1867, in an exhaustive description of the contents 

 of vegetable cells, states distinctly that the nucleus arises from 

 homogeneous protoplasm, and that in all cell-division the nucleus 

 must first disappear, two new ones arising in its place. The 



nucleus occupied a secondary place as a derivative organ ; and the 

 chlorophyl granules were believed by him and his contemporaries, 

 to be new formations from homogeneous protoplasm under certain 

 conditions of light, temperature, and food. Researches which 

 leave no room for doubt have shown that the nucleus, in all cases, 

 hitherto examined, springs from a pre-existent nucleus by a process 

 of division. The process of division, with its marvellous sequence 

 of formal arrangements of definite portions in meridional lines and 

 in polar and equatorial masses, has been most carefully examined' 

 in almost every organ of the plant, and in connection with similar 

 processes of cell-division in animal tissues. In no well-marked 

 case has a nucleus been observed to arise from homogeneous pro- 

 toplasm, even a few doubtful instances having been lately explained' 

 satisfactorily. 



The extraordinary manner in which the nucleus, both in common, 

 cell-divisionand in reproductive blending, carries ancestral char- 

 acters and controls the distribution of nutritive materials, is as yet 

 the greatest mystery in vegetable life. 



We pass next to consider a very important change of view in re- 

 gard to the other granules embedded in the protoplasmic body,, 

 known as leaf-green or chlorophyl granules. Formerly, as we have 

 noticed, it was held that all of these sprang by a process of differ- 

 entiation from the shapeless mass in each exposed cell. Researches, 

 by Schmitz on some of the lower plants, and by Schimper and 

 Meyer on the higher, have shown beyond any reasonable doubt 

 that these chlorophyl granules always arise by a process of divis- 

 ion from pre-existent granules ; but this fact, taken by itself, might 

 not possess great interest. It is, however, known, that, at the growing 

 points where leaves are developed, the cells contain in their proto- 

 plasm granules of about the consistence and color of protoplasm^ 

 itself ; and these granules have the power of division, much after 

 the fashion of the cell nucleus. But the products of such divisiort, 

 are essentially threefold : some of the resulting granules are color- 

 less, like the mother granules ; others become true chlorophyl 

 granules ; while others still, in those leaves which become the 

 leaves of the flower and the fruit, assume colors other than green.. 

 In other words, we have in these associated granules, or chromato- 

 phores, a morphology which is of the highest interest. The needs- 

 of the plant bring from this common source the microscopic organs, 

 for assimilation, for storing- up starch in the form of grains, for 

 protection and attraction. This most interesting generalization ia 

 regard to the granules taken together adds a new zest to the study 

 of the developing plant and the evolving species. 



It has been lately claimed by De Vries of Holland that the sap- 

 cavities or vacuoles in protoplasm divide in much the same way as. 

 do the granules just referred to, but this part of the subject is not 

 yet beyond all doubt. That the sap-cavities are the birthplace of 

 most crystals, and that the aleurone grains may be desiccated sap)- 

 cavities, has been made out by several observers. But it is not 

 clear that vacuoles divide as granules do. What we do know be- 

 yond all reasonable question is this, — that all the working granules, 

 within the plant have sprung from pre-existent granules, and that 

 there is no break here in the transmission from parent to offspring.. 



Such, then, are some of the more important changes which have 

 taken place with regard to our knowledge of the living contents of 

 vegetable cells. I would gladly take the time, if it could be- 

 granted, to call your attention to certain most interesting discoveries, 

 which have been made by Pfeffer, relative to the absorption of 

 coloring-agents by living protoplasm, and which have been supple- 

 mented by Campbell in regard to the nucleus ; but more than this. 

 allusion is now impossible. 



It is an interesting coincidence that with the substitution of the- 

 crude compound microscope for high-power simple lenses, in 1660,. 

 came the first works on vegetable structure ; and for more than 

 one hundred years, or until the introduction of achromatic object- 

 glasses, these works were, in truth, the only authoritative treatises.. 

 With the introduction of water-immersion lenses came renewed 

 activity in this field, and with the later discovery of homogeneous 

 immersion lenses came the results which have now been detailed. 

 Whether we have, at these stages, more than a series of interesting 

 and very striking coincidences, or not, we have not time now to 

 discuss. It is enough for our present purpose to observe, that,, 

 with the introduction of the cedar-oil immersion objectives, a 



