ZOOLOGY AND BOTANY, MICBOSGOPY, ETC. 407 



the primary cortex of first-year twigs of Cornus mas, Ligustrum 

 vulgare, and Staphylea pinnata ; in the small intercellular spaces 

 between the collenchymatous peripheral cells of the leaf-hinge of 

 Epimedium alpinum and of the leaf-stalk of Pittosporum Tobira ; in the 

 primary cortex of Bhus glabra, &c. In order to detect this inter- 

 cellular protoplasm, uninjured pieces of the plant must be laid in 

 alcohol, or must be first hardened in potassium bichromate. One of 

 the best objects is Ligustrum vulgare, where the small intercellular 

 spaces of the young leaves of the winter-buds, as well as those 

 between the young medullary cells, may be found to be filled with a 

 protoplasmic substance. 



Division of the Cell-nucleus.* — The following are the main results 

 of a series of experiments on this subject by E. Heuser : — 



The only point which distinguishes the material of the nucleus 

 from the surrounding protoplasm is that it consists to a large extent 

 of nuclein. When at rest the substance of the nucleus consists of 

 granules of various sizes imbedded in the nuclear hyaloplasm which 

 has the form of a framework composed of strings. The granules do 

 not all agree in chemical and physical properties. The nuclear 

 hyaloplasm is surrounded by nuclear sap, apparently identical with 

 the cell-sap, and is in continuous connection with the cyto-hyaloplasm 

 through the membrane of the nucleus. The nuclear membrane con- 

 sists of an extremely fine-meshed net of cyto-hyaloplasm, in which a 

 few microsomes may be imbedded. This network is entered on one 

 side by the delicate threads of cytoplasm, on the other side by the 

 fine strings of the interior of the nucleus. 



The nucleoli are larger collections of nuclear hyaloplasm, which 

 serve as reservoirs for the substance of the nucleus, possibly in solution. 

 The substance of the nucleus is divided, even while it still has 

 the form of a ball, transversely into a number of loops. A further 

 segmentation also occurs in the pollen-mother-cells of Tradescantia. 

 The loops consist of nuclear substance, which, both in this condition 

 and in that of rest, is surrounded by a sheath of hyaloplasm. These 

 sheaths are still partially connected with one another after the trans- 

 verse division of the substance of the nucleus, but afterwards only 

 with the nuclear membrane. Immediately after the disappearance of 

 this membrane, the threads of the hyaloplasmatic figure (the spindle- 

 fibres of Strasburger and the achromatic figure of Flemming) arise out 

 of the sheaths of hyaloplasm by the addition of cyto-hyaloplasm. 



The elements of the nuclear substance, before splitting longitudi- 

 nally into the equatorial plate of Strasburger, are not distributed 

 equally on both sides of the equator ; there cannot therefore have been 

 up to this time any " double decomposition " of the equatorial plate or 

 bisection of the nucleus. To render possible the formation of two 

 daughter-nuclei of equal size a further complete division of the 

 nuclear substance must therefore take place. This is effected by 

 longitudinal splitting and re-disposition of the elements under the 

 influence of the hyaloplasm, which is applied as " spindle-fibres " to 



* Bot. Centralbl., xvii. (1884) pp. 27-32, 57-9, 85-95, 117-28, 154-7 (2 pis.). 



