ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 259 



its cells contains dark particles soluble in ether, chloroform, and 

 especially in bisulphide of carbon. These particles disappear when 

 the organism is transferred to water destitute of sulphates, and can be 

 seen, on the other hand, to be formed within filaments in liquids rich 

 in calcium sulphate. They are uncrystallizable, and consist simply 

 of a deposit of sulphur. 



The large blue filaments of Oscillaria were found to possess a 

 similar property of withdrawing sulphur in the form of very fine 

 granulations from water containing sodium or calcium sulphate in 

 solution; while very fine filaments of the same alga appeared to 

 possess no such power. Two species of Ulothrix presented similar 

 phenomena. 



The exhalation of sulphuretted hydrogen from sulphurous waters 

 is, then, due to the power possessed by these algee of removing sulphur 

 from the sulphates contained in solution in them. The organic matter 

 in these waters consists of these low organisms, and is not, as fre- 

 quently stated, contained in solution, becoming insoluble only on 

 exposure to the air. 



Morphology of Marine Algse.* — G. Berthold enters into a very 

 detailed description of the morphology and physiology of certain 

 marine algae in respect to the following points : — 



1. Heliotropism. The observations relate especially to Anti- 

 ihamnion cruciatum, Derhesia marina, and Ectocarpus humilis. In 

 addition to ordinary positive and negative heliotropism, Darwin and 

 Frank assume the existence of a third force, which they call diahelio- 

 tropism or transverse heliotropism, in virtue of which the growing 

 point places itself at right angles to the incident rays of light. 

 Berthold sees no necessity for this assumption. 



2. The factors that determine the structure and mode of growth 

 of the thallome of algae. The algge specially investigated are 

 Antithamnion cruciatum, Pterothamnion Plumula, and Spermothamnion 

 flahellatum. They refer especially to dorsiventral curvature in 

 reference to the effect of light. 



3. Contrivances for protection against too intense illumination, 

 with special reference to Chylocladia, Chondriopsis, and Bryopsis. 

 These consist of different forms of hair, belonging to several different 

 types which characterize different families. A similar object is 

 gained by the strongly refractive substances contained in the proto- 

 plasm which give to many algse their brilliant appearance. The 

 calcareous deposit in the thallome of Corallina, Halimeda, &c., 

 answers a similar purpose. 



Vaucheria.t — Dr. M. C. Cooke writes that the structure and 

 development of Vaucheria has been so often and so well studied and 

 illustrated that the observation of any new feature is quite unexpected, 

 and will encounter some opposition, or at least excite some doubt. 

 One of the generally accepted conclusions is, that the threads of 

 VaucJieria are continuous throughout their length, only presenting 



* Pringsheim's Jahrb. f. Wiss. Bot., xiii. (1882) pp. 569-717 (4 pis.). 

 t Grevillea, xi. (1883) pp. 104-6 (1 pi.). 



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