NATURE 



\Nov. 



themselves are not passive, but possess a movement of 

 their own held in control by polar influences. 



For details relating to the complicated transpositions of 

 the fibrils, their longitudinal fission, and subsequent sepa- 

 ration, the reader is referred to Chapters VII. and VIII. 



The two groups of daughter-segments separate, the 

 segments travelling along the filaments of the spindle. 

 Prof. Strasburger considers the hypothesis that the travel- 

 ling is due to streaming of the protoplasm improbable, as 

 this would involve the running of two opposite currents 

 in each spindle-filament. Further, no streaming, either in 

 or on the filaments, has been observed in the living, divid- 

 ing nucleus. The fibrils themselves probably possess a 

 capacity for movement, using the spindle-filaments only 

 as supports. What stimulus the segments may receive 

 from the poles is difficult to say — perhaps one similar to 

 the chemical stimulus which causes directive movements 

 in Bacteria, Plasmodia, &c. As the groups of daughter- 

 segments move apart, the spindle-filaments, which are 

 continuous from pole to pole, on the view of Strasburger, 

 are seen stretching over the interval. These constitute 

 the primary uniting-filaments, and there is some diversity 

 of opinion as to their origin. Soon, more cytoplasm makes 

 its way into the equatorial region, and a great increase in j 

 the number of the filaments takes place. These additional, ' 

 or secondary, uniting-filaments are formed from this in- ■ 

 trusive cytoplasm, and not by multiplication of the primary \ 

 ones. ^ ' 



The nuclear sap, and dissolved nucleoli, lie between ! 

 the uniting-filaments ; and even after the collection toge- \ 

 ther of the daughter-segments to form the daughter-nuclei, ' 

 there remains a considerable residuum of stainable nuclear 

 sap which makes its way to the equatorial region of the ' 

 spindle and appears to play a most important part. j 



At this moment a small bead-like thickening appears ! 

 on each uniting-filament — both primary and secondary — I 

 in the equatorial plane, and it is by the fusion of all these ! 

 thickenings that the cell-plate or primitive cell-membrane j 

 arises. Throughout, Prof. Strasburger speaks of this 

 occurrence with the greatest confidence, in opposition to 

 the view of Zacharias and Flemming. These swellings i 

 which constitute the elements of the cell-plate, are spoken ! 

 of as dermatosomata, although the same word has been \ 

 recently used by Weisner with another significance. Fresh ' 

 uniting-filaments continue to arise at the periphery of the 

 young cell-plate, each bearing a local swelling [dermato- | 

 some), and in this manner the cell-plate is completed 



possesses also the added charm of simplicity. The chief 

 objection to this theory is the difficulty in imagining the 

 continued presence of the nuclear sap in regions where 

 the cell-wall is undergoing a thickening ; for will not the 

 process of conversion throughout be identical, whether it 

 be primary or secondary layers that are being formed ? 

 Perhaps in a future contribution this will be explained ; 

 but for the present this hypothesis must remain a hypo- 

 thesis, and will — be it hoped — stimulate investigation 

 into a matter on which more light is much needed. 



As the daughter-nuclei are formed, a considerable 

 portion of the nuclear sap is taken in, and lies, in the 

 first instance, on the antipolar side of the nucleus, where in 

 some few cases (embryo-sac of Hyacitithus orientalis) the 

 nucleoli appear, and the sap loses its staining property. 

 In the majority of cases the nucleoli, as stated above, 

 appear towards the polar side. 



In a chapter dealing with the function of the nucleus 

 the view is put forward that it has the same relation to 

 starch-formation as very probably exists between it and 

 the development of cell-membrane. The fact that Klebs 

 found, in plasmolyzed filaments oi Spirogyra, a formation 

 of starch occurring in masses of protoplasm destitute of 

 a nucleus. Prof Strasburger considers due to the fact 

 that the pyrenoids physiologically replace the nucleus in 

 this connection. This finds support in the fact that in 

 plasmolyzed cells oi Funaria the chlorophyll-corpuscles in 

 fragments of cells without a nucleus are unable to form 

 starch. 



The book concludes with a chapter on fertilization, in 

 which controversial matters are discussed. The author 

 adheres to his former view that in higher plants fertilization 

 consists of the fusion of an equal number of nuclear 

 segments, as also of the nuclear sap of the two conjugat- 

 ing nuclei. He finds no evidence for the view of 

 Zacharias that the male and female nuclei differ 

 essentially in any way. 



It is impossible here to do full justice to this remarkable 

 book, and there are many matters traversed in it to which 

 we have not even alluded. Thus, the detailed comparison 

 drawn between the vegetable and the animal nucleus. It 

 seems that the differences in this respect occurring be- 

 tween lower and higher plants find their parallel in com- 

 parable differences in more lowly and more highly 

 organized animals. 



A careful perusal of the original will repay the labour 



,..;, ... ....„ _- . J- r so expended, and the style and arrangement of the subject- 



In cases of free-r ell-formation a temporary cell-plate ap- j matter are such as to make us unwillingly lay it aside. 



pears, but is not completed, and subsequently disappears. 

 It is at this stage that Prof. Strasburger attaches great 

 importance to the part played by the stainable nuclear 

 sap. As above mentioned, a portion of this has collected 

 in the equatorial region, and everywhere bathes the 

 dermatosomata. At the same time a demonstrable 

 change takes place in their constitution ; the dermato- 

 somata offer a greater resistance to such a reagent 

 as eau-de-javelle, and show an increased refrangibility. 

 In other words, the cell-plate has been converted into the 

 first layer of the new cell-wall. These changes are traced 

 to the stainable nuclear sap which is present. A direct 

 proof of this is very difficult, but the hypothesis is a most 

 taking one ; accounting, as it does, for a number of 

 phenomena which have long baffled explanation \ and it 



Perhaps some idea of the pace at which knowledge in 

 minute cell-histology has progressed may be obtained 

 when we remember that only seventeen years ago a 

 botanist, who now stands in the foremost rank of plant- 

 histologists, was prepared to maintain as a thesis, and to 

 dispute with all comer?, " that in the vegetable kingdom 

 nuclear division does not occur. ' F. W. O. 



OUR BOOK SHELF. 



Chambers's Ency, lopcedia ; a Dictionary of Useful 

 Knowledge. New Edition. Vol. II. (London and 

 Edinburgh.: W. and R. Chambers, 1888.) 

 The second volume of the new edition of " Chambers's 

 Encyclopaedia," which extends from " Beaugency " to 

 " Cataract," maintains the high standard set by the 



