314 Algae. 



losing their apical cells, actively produce lateral brancheswhich unite 

 them together the more firmly. Dying off in the centre, the balls 

 tend to becotne hollow, and in April and May contain enough gas 

 within to raise them to the surface. At other times of the year the 

 plankton of the waters provide a screen dense enough to prevent 

 füll light from penetrating the waters; and the balls are unable to 

 rise to the surface. E. S. Gepp. 



Acton, E., Studies on Nuclear Division in Desmids. I. 

 Hyalotheca dissiliens (Sm.) Breb. (Annais of Botany. XXX. 119. 

 p. 379—382. 1 pl. and figs. July 1916.) 



With few exceptions, Desmids do not tolerate artificial condi- 

 tions, and therefore cannot be cultivated with success; and it is a 

 matter of chance that they should be found undergoing division 

 under natural conditions. Hyalotheca was obtained in sufficient 

 quantity to yield complete results, but unfortunately its nucleus is 

 too small to show all that is desired. In its nuclear division granu- 

 les appear on the network and become larger and fewer, while 

 the nucleolus disappears; these stages are obscure, but probably 

 the chromosomes are being formed on the spireme. Then about 

 twelve Short broad chromosomes are seen collected on the equato- 

 rial plate; fibres, but no definite spindle, can be made out. These 

 stages are all figured, also the metaphase, anaphase, and telophase. 

 In the daughter-nuclei the chromosomes disappear, granules appear 

 and gradually fuse to form the large nucleolus. 



The daughter-nuclei move asunder at once and become situated 

 opposite the pyrenoids. Formation of the new cell-wall was not 

 observed in detail; but it is always completed before the division 

 of the chromatophore begins. As the chromatophore divides the 

 nucleus slips in between the two halves until it finally reaches the 

 pyrenoid and, during the division of the pyrenoid by constriction, 

 reraains firmly pressed up against it. Division of the chromatophore 

 and pyrenoid is probably largely influenced by the presence of the 

 nucleus The starch sheath of the pyrenoid is not markedly affected 

 until chromatophore division begins the starch sheath then rapidly 

 sinks and disappears. The presence of a large störe of starch in 

 the cell is not in itself sufficient to induce nuclear division. 



E. S. Gepp. 



Svedelius, N., Das Problem des Generationswechsels bei 

 den Florideen. (Natw. Wschr. N. F. XV. p. 353—359. 372-379. 

 ill. 1916.) 



Die Bedeutung der Reduktionsteilung liegt nicht ausschliesslich 

 darin, dass die ursprüngliche Chromosomzahl wiederhergestelt wird, 

 sondern auch darin, dass durch sie Neukombinationen von Chromo- 

 somen in den Tochterkernen entstehen, was bei den somatischen 

 Aequationsteilungen ausgeschlossen ist. Die Reduktionsteilung spielt 

 bei der Neukombination von Chromosomen im Kerne eine ebenso 

 wichtige Rolle wie die Befruchtung selbst, als deren Schlussakt sie 

 aufgefasst werden kann. Denn in ebenso hohem Grade, wie durch 

 die Befruchtung selbst die Möglichkeit neuer Kern- und damit 

 Chromosomzahlkombinationen gegeben ist, ist durch die Reduktions- 

 teilung eine Möglichkeit für neue Kombinationen von Chromosomen 

 innerhalb der Kerne geschaffen. 



Bei den Florideen, auf die Verf. besonders ausführlich ein- 



