74 SUMMARY OF CURRENT RESEARCHES RELATING TO 



ture and development of the cell of a centrifugal force varying from 

 1700 to 1930 times that of gravity. The objects experimented on were 

 Cladophora, Spirogyra, and other fresh-water algfe, Cham and Nitella, 

 staminal hairs of Tradescantia and other trichomes, leaves of mosses, 

 ■&c. In Cladophora, the effect of the treatment was that almost the 

 entire contents except the parietal utricle were crowded into a dense 

 mass at the end of the cell, and yet the vitality of the cell was in no 

 way injured ; after the lapse of a considerable time the contents again 

 took up their normal position. With Spirogyra the general results 

 were the same, but the cells were much more liable to injury in the 

 process. Cell-division may commence, in both cases, before complete 

 redistribution of the contents is accomplished. The author regards his 

 results as confirmatory of the view that in both types of cell-division 

 represented by Cladophora and Spirogyra, a close relation exists be- 

 tween the nucleus or nuclei and the transverse membrane in process 

 of formation. 



Plasmolysis of Growing Cells.* — From a series of experiments on 

 a variety of plants, both cryptogamic and phanerogamic, Herr M. O. 

 Bernhardt derives the conclusion that in the growth of the cell-wall 

 there must be a mutual reaction between the protoplasm and the young 

 membrane, the source of which must lie partly in the membrane, though 

 it can be brought into action only by the co-operation of living proto- 

 plasm. The relations between membrane and protoplasm may be 

 brought about by delicate threads of protoplasm connecting the proto- 

 plasts with the micellae of the cell-wall. When this delicate connection 

 is ruptured by plasmolysis, it cannot be restored, and growth must cease. 

 The protoplasm receives the stimulus and reacts upon it, determining 

 the form and the direction of growth ; but there are also active forces 

 in the cell-wall, which possibly act in the manner suggested by Nageli 

 in his theory of intussusception. 



Centrifugal Growth, of the Cell-wall and Extracellular Proto- 

 plasm, f — The growth on the outside of the cell-wall is very much 

 less common, and has been much less carefully investigated, than the 

 ordinary centripetal growth. Herr F. Schiitt has studied it in the 

 cases of the Peridinieas (Ceratium and Podolampas), diatoms (Cyclotella 

 socialis), and desmids. The bands, spines, wings, &c, which occur 

 outside the cell-wall in the Peridinieas, cannot be derived from the 

 internal protoplasm, since neither intussusception nor apposition could 

 account for their formation in this way. The explanation otfered is 

 that these structures have their origin in a portion of the protoplasm 

 which has escaped from the interior of the cell, passing through the 

 sieve-like pores which everywhere perforate the cell-wall. From the 

 occurrence of this phenomenon the author groups together the three 

 families named under the term Placophytes. 



In the case of the Peridinieas named, as well as some others, the 

 author has detected very fine threads passing through the pores in the 

 cell-wall to which he attributes a protoplasmic character, as well as 



* Festschr. f. Schwendener, 18D9, p. 124 (1 pi.). See Bot. Ztg., lvii. (1890) 

 2 te Abth., p. 298. 



t Pringsheim's Jahrb. f. wiss. Bot., xxxiii. (1899) pp. 594-690 (3 pis.). 



