136 Botanisches Centralblatt. — Beiheft 2. 



color, wliile tiie cytoplasm is of a browuish hue. The cytoplasm 

 presents a regulär Hbrillar or alveolar arrangement, (Figs. 1 and 

 3.) The meshes especially in the younger cells are very small 

 and their regularity in many cases is very striking. The cyto- 

 plasm , however , does not retain its homogeneous structure 

 throughout the entire course of karyokinesis. By the time the 

 splindle is matiire that portion of the cytoplasm immediately 

 surrounding it has become very dense while the remaining 

 cytoplasm reveals larger meshes and is less granulär. In width 

 this layer of protoplasm extends one half the distance across the 

 cell (Figs. 3, 4, 5). Its margin is deeply wavy so that at places 

 it approaches quite near the cell-wall. The remaining protoplasm 

 of the cell has also changed for its meshes (Fig. 4) appear to be 

 five or six times as large as they were in the earlier stages. The 

 regularity of the protoplasmic meshes are now clearly less regulär 

 in outline. An examiuation of hundreds of specimens confirmed 

 the above Statements in every case. 



Development of the chromosomes. 



In the very early stages the nucleus, as above stated, pre- 

 sents a fine linin net. The threads of the net are at first smooth 

 and uniform in diameter. In nuclei, however, which have ad- 

 vanced slightly beyond the resting stage the linin-net begins to 

 show irregularities in Avidth due to the appearance of larger 

 granules. These granulär masses constitute the chromatin. They 

 are irregularly distributed in the linin net-work, and increasing 

 in size ultimately form the chromosomes. A continuous chromatin 

 spirem does not seem to be developed in MagnoUa. It Avill be 

 seen further that the nucleolus at this stage (Fig. 1) is very large 

 staining densely and contains a conspicuous vacuole. The Hbres 

 of the linin network run to the nucleolus and are attached to it 

 in such a way that a slight enlargement at the point of contact is 

 visible. This was always found to be the case Avhether one or 

 several nucleoli were present. These filiaments radiating from 

 many points on its periphery seem to hold it in position. Its 

 Position was influenced in the direction of attachment of the 

 greatest number of nuclear fibres (Fig. 1). 



At a later stage of karyokinesis (Fig. 2) we find that the 

 nucleolus has entirely disapeared. It is probably utilized as food 

 in the growth of the chromatin masses, for they stain much more 

 readily and intensely at this time than at an earlier stage. The 

 nuclear membrane which is now less distinct is gradually replaced 

 by a weft of filaments closely interwoven. The threads of this 

 weft are very line, and the most careful staining is necessary to 

 bring them out. 



The different forms which the chromosomes assume at this 

 stage (Fig. 2) are due to a total or partial longitudinal Splitting 

 and a subsequent bending. This longitudinal cleavage is recoguized 

 as a rather clear line which appears through the length of the 

 chromosorae (Fig. 2). After this division the chromosomes bend 



