116 



1 



The details* of the nuclear changes are not very easy to fol- 

 low, but such stages as shown in PL CII. Fig. 8 are often met 

 with. We find in such the division wall forming in the same way 

 as in Cladophora, but near the center of the cell-lumen we find 

 two daughter-nuclei suspended by protoplasmic threads and 

 joined by numerous fine filaments, the outer ones of which are 

 attached to the margins of the advancing division wall. The 

 protoplasmic body of the cell is cut through in precisely the same 

 way as in Cladophora, and finally the daughter nuclei move to 

 the centers of the new cells. 



The various desmids, especially the forms with constricted 

 cells, show an interesting modification of the process observed in 

 Spirogyra, Desmids are especially common on such fine-leaved 

 aquatics 2.sNaias, Nitella^Chara, and especially Utricularia, whose 

 finely dissected leaves are often In late summer and autumn loaded 

 down with all sorts of micro-organisms, among which are many 

 of the most beautiful desmids. With a little care these maybe 

 kept In glass jars or other convenient vessels and will thrive for a 

 long time. In such cultures they are not infrequently met with 



undergoing division, which occurs at all hours of the day. 



The first sign of approaching division Is the elongation of the 

 neck connecting the semi-cells. A circular split in the wall is 

 formed at this point and widens rapidly, forcing the original semi- 

 cells apart, when these appear connected by a slender, colorless 

 cylinder with much thinner walls than the original semi-cell. As 

 this connecting cylinder enlarges It soon becomes constricted in 

 the middle, and a division wall is formed much as in Spirogyra, 

 this being accompanied by the division of the centrally placed 

 nucleus. As division proceeds the two halves of the colorless neck 

 enlarge rapidly, forming colorless vesicles lying between the ori- 

 ginal semi-cells which as yet contain all the colored contents of 

 the cells. (Such a stage is shown in PI. CII. Fig. 9). Here we find 

 that the single large chloroplast in each half of the original cell is 

 becoming constricted as well as the pyrenold (p.) imbedded in 

 it, and that the nuclear division is completed. In a somewhat 

 later stage the lower halves of each chloroplast push down into 

 them, and finally separate completely from the part that remains In 

 the old semi-cell. 



*Slrasburger — Das BotuuUclic Practicum — p. 612 1st. Edit. 



