810 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tion of the intermediate substance and of the entire volume of the 

 nucleus. The cell-plates are formed in the same way as in other 

 pollen-grains ; but the arrangement of the daughter-nuclei differs 

 somewhat from the normal, since they lie either in a plane or 

 cross-wise. The special mother-cells sometimes undergo subsequent 

 divisions, resulting in the formation of smaller pollen-grains. 



Comparing this development with that of the animal ovum, the 

 author considers the small globular structures or nucleoli, which 

 often accompany the primary nucleus of the mother-cells when 

 reduced by retrogressive metamorphosis, to be the homologue of the 

 elements of the germinal vesicle which are not active in the formation 

 of the bi-aster. 



Structure and Growth of the Cell-wall.* — Professor E. Stras- 

 burger's most recent publication is divided into the following 

 sections : — The origin and growth in thickness of the cell-wall ; the 

 growth of starch-grains ; the relationship of swelling to anatomical 

 structure ; the formation of membrane in the animal kingdom ; the 

 double refraction of organized structures ; the molecular structure of 

 organized bodies ; the assimilation of carbon ; the function of the 

 cell-nucleus ; the permeability of the cell-wall ; and the behaviour of 

 the cell-nucleus in the process of sexual reproduction. The following 

 are some of the more important results at which he has arrived : — 



With regard to the intimate structure of organized bodies, Prof. 

 Strasburger entirely dissents from Naegeli's micellar hypothesis. 

 This hypothesis was based upon the phenomena of " swelling-up " 

 which are so characteristic of organized bodies, and upon the optical 

 properties which certain of these bodies possess. Professor Stras- 

 burger points out that swelling-up may be as well ascribed to the 

 taking-up of water between the molecules of the body as to its being 

 taken up between Naegeli's micellae. He shows also that the double 

 refraction of organized bodies, such as cell-walls and starch-grains, 

 depends upon their organization as a whole ; for when once their 

 organization is destroyed, their double refraction is lost, a result 

 which cannot be explained on the micellar theory, since the particles 

 of the disintegrated micellae would, like particles of broken crystals, 

 still retain their power of double refraction. According to Stras- 

 burger the molecules of an organized body are not aggregated into 

 micellae which are held together by attraction, but are linked together, 

 probably by means of multivalent atoms, by chemical affinity, in a 

 reticulate manner. Swelling-up is then the expression of the taking- 

 up of water into the meshes of the molecular reticulum, where it is 

 retained by intermolecular capillarity. The more extensible the 

 reticulum, that is, the more mobile the groups of molecules within 

 their position of equilibrium, the greater the amount of swelling-up. 

 The limit is reached when the chemical affinity of the molecules and 

 the force of the intermolecular capillarity are equal ; if the latter 



* Strasburger, E., ' Ueber den Bau u. das Wachstkum der Zellh'aute.' 264 pp. 

 (8 pis.) Jena, 1882. Cf. also article by Dr. S. H. Vines in ' Nature,' xxvi. (1882) 

 p. 595, and Bot. Centralbl., xi. (1882) pp. 269-83. 



