ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 665 



of nitrogen than fronds from pure sea-water in the corresponding season. 

 The result of this excessive nourishment is seen in an increased rate of 

 growth, the fronds being at the same time of a different texture and of 

 a darker colour. But, as in other cases of over-fed plants, there is a 

 tendency for spore-formation to remain in abeyance, ami increase to take 

 place by vegetative methods; the growth, therefore, may be considered 

 as rank rather than healthy. With regard to the Belfast nuisance, the 

 author considers that since Ulva is not dependent on sewage, it will not 

 be suppressed until the mussels are exterminated. 



Spirogyra.* — F. M. Andrews records an instance of conjugation 

 taking place between Spirogyra crassa and S. communis. A large 

 quantity of the two species was found in a pond and all stages in the 

 process of conjugation could be seen. In most cases the same species 

 conjugated together, but in many cases the two species cross-conjugated. 

 As a rule the contents of S. communis passed over to S. crassa, but 

 instances of the opposite mode were also found. Both cases are figured. 

 Apart from a difference in size and form, the zygospores seemed perfectly 

 normal. The author writes from Indiana University, Bloomington, U.S.A. 



Desmids of the Burgaschimoos.t — F. Miihlethaler writes on the 

 I )es in id-flora of the Burgaschimoos, a locality already well worked for 

 flowering plants. He records ninety-five species and varieties, collected 

 during March and April in last year. Although no new species are 

 formally described, the author gives details of certain species and forms 

 which he finds vary greatly from those already known, and he believes 

 that they will prove to be novelties. A section of the paper is devoted 

 to a short discussion of the ecological conditions, and remarks on the 

 other components of the cryptogamic flora found there. The list of 

 Desmids is finally given in tabulated form, showing the occurrence of 

 each species. 



Cell and Nuclear Division in Closterium.J — B. F. Lutnian has 

 made a study of the cell and nuclear division in Glosterium, and describes 

 the results at length. The summary given is as follows : 1. Closterium 

 divides from 10 p.m. to 5 a.m., and the new half has become practically 

 symmetrical with the old one by 9 a.m. 2. Division is dependent upon 

 the storage of a considerable quantity of starch in the chromatophore 

 and around the pyrenoids. 3. The chromatophore divides by a con- 

 striction located about a third of the distance out from the middle. 

 This constriction is due to the enlargement of a ring-shaped vacuole 

 under the plasma membrane. 4. The resting nucleus of G. Ehrenbergii 

 is made up of a very fine reticulum carrying little if any chromatin in the 

 form of granules. At the centre of this reticulum is a large compound 

 nucleolus made up of a number of partially fused nucleoli. The resting 

 nucleus of C. moniliferum has essentially the same structure, but the 

 nucleoli at the centre are more completely fused. 5. The spireme is 

 formed outside the nucleolus and apparently separate from it. During 



* Bull. Torrey Bot. Club, xxxviii. (1911) p. 299 (1 fig.). 



t Mitteil. Naturf. Gesell. Bern (1911) pp. 101-22 (figs, in text). 



X Bot. Gazette, li. (1911) pp. 401-30. 



