ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 979 



iu the parietal layer of tlie embryo-sac otLeucoJuvi sestivum are described 

 in detail. The nuclei are first of all enveloped in denser protoplasm ; 

 but before the absorption of the cellular membrane a spindle-like dif- 

 ferentiation of this mass of protoplasm may be perceived. Strasburger 

 shows that the microchemical reactions of the nuclear spindle by no 

 means oppose the theory of its origin from the cytoplasm. 



(8) The separation of the secondary segments. In opposition to his 

 previous views, the author now agrees with Heuser and Guignard that 

 the separation of the halves of the segments within the cells of higher 

 plants always takes place so that the end of each half-segment which is 

 directed outwards points immediately after the separation towards the 

 equatorial plane. 



(9) Absorption of the nucleoli. The diiferences in the capacity of 

 the nuclear filaments for absorbing pigments observed by Went do not 

 always coincide in time with the disappearance or reappearance of the 

 nuclei ; and it is improbable that the nucleoli contribute to the nutrition 

 of the nuclear filaments. 



(10) Uniting-threads and cell-plate. In opposition to the recent 

 views of Berthold and Zacharias, but in agreement with those of Gui- 

 gnard, Strasburger shows that, in the higher plants, the spindle-fibres 

 always go from pole to pole, and pass over afterwards into the so-called 

 uniting-threads, the number of which can, however, gradually increase 

 considerably at the expense of the cytoplasm. In their chemical re- 

 actions these threads agree altogether with the spindle-fibi'es. In cells 

 which contain but little protoplasm, these threads form a more or less 

 thick continuous tube extending from one of the two daughter-nuclei to 

 the other, which becomes gradually more and more stretched by the 

 growth outwards of the membrane. 



(11) Origin of the membrane. The new membrane arises by the 

 fusion and chemical metamorphosis of the dermatosomes, which are at 

 first simply thickenings of the uniting-threads. 



(12) Formation of the nucleoli in the daughter-nuclei. With the new- 

 formation of the nucleoli the nuclear saj) loses its capacity for absorbing 

 pigments. 



(13) Part played by the nuclear sap and nucleoli. Prom the facts 

 that the nuclear sap becomes receptive for pigments on the disaj^pearance 

 of the nucleoli during karyokinesis, and that strongly receptive sub- 

 stances accumulate in the neighbourhood of the cell-plate before the 

 formation of the new membrane, Strasburger concludes that the substance 

 of the nucleoli takes part in the formation of the new membrane. 



Herr E. Zacharias* discusses in detail Strasburger's observations, 

 controverting some of his conclusions. He regards Strasburger's expla- 

 nation of the changes in the nuclear threads, viz. that they result from 

 the opposition of forces in different directions operating within and 

 without the nucleus, as being but imperfectly founded on facts. He dis- 

 putes the accuracy of conclusions drawn from preparations of nuclei in 

 the knot-condition treated with alcohol or chromacetic acid and stained 

 by safranin or hgematoxylin, since all parts of the nucleus are not brought 

 out clearly and definitely. Nor can Strasburger's negative results of 

 treatment with methyl-blue and eau de Javelle be set against Zacharias's 

 previous results obtained by other means. Zacharias repeats his previous 



* Bot. Ztg., xlvi. (1888) pp. 437-50, 453-60 (4 figs.). 



