76 



The Nucleus. 



The presence of nuclei in the cells of the higher plants has 

 long been known to be of the greatest importance to their life 

 and development. The exact function of the nucleus is at 

 present unknown, but looking at its extreme complexity of 

 structure and the complicated changes which take place in it 

 during the growth and division of a cell, it must be an impor- 

 tant one. It becomes, therefore, a point of considerable interest 

 to determine whether the cells of the lower plants contain nuclei 

 or not, and also whetlier they have a structure and undergo 

 changes comparable with what is found in the nuclei of the 

 higher plants. As regards the presence of the nuclei in the 

 lower plant cells, we are now able, thanks to the researches of 

 Schmitz,! Zacharias,- Scott,-' and others, to show that the cells of 

 all plants, with the exception of the Bacteria, contain one or 

 more nuclei ; and the same may be said of the animal kingdom. 

 It should be remarked, liowever, that the nuclei in these lower 

 plants are so small that it becomes a matter of some difficulty 

 to distinguish them from other small bodies contained in the 

 protoplasm. Dr. Schmitz,* who in 1879 announced that he had 

 been able to show the presence of nuclei in the cells of all 

 Fungi, relied largely upon the fact that when placed in a staining 

 solution such as haematoxylin, the nuclei become more deeply 

 stained than the remainder of the protoplasm. This method of 

 distinguishing them from the other granules in the protoplasm 

 is, however, hardly satisfactory, because the granules take the 

 stain as well as the nuclei ; moreover, it sometimes happens that, 

 owing to defective methods of preparation, the protoplasm forms 

 roundish deeply-staining coagulations, which may be easily mis- 

 taken for nuclei. There is, in fact, at the present day no decisive 

 test for nuclei, except the morphological one of structure. 

 Zacharias and others have, it is true, done much to show that 

 the presence of a nucleus may be determined by chemical means, 

 but their tests, although they are extremely valuable, are not so 

 much tests of the presence of a nucleus as of the presence of 

 nuclear substance; and, as has been pointed out, the nuclear 

 substance may be dissolved in the cell protoplasm. Althougli 

 much may be done in the future, from the chemical side, it is, 



Sitzgsber d. Niederrh. Ges., 1879. - Bot. Zeitimg, xlv., 1887. 

 3 Linn. Soc. Journal Bot., 1887. * Loc. Cit. 



