212 SUMMARY OF CURRENT RESEARCHES RELATING TO 



another piece of evidence showing that there is no hard and fast line 

 between Euglena and Astasia. In darkness the chromatophores appear 

 as small leucoplasts, in light as large chloroplasts ; the colourless phase 

 thus becomes green, and its heterotrophic diet becomes mixotrophic or 

 autotrophic. The colourless form may arise from the green form : — (a) in 

 organic nutritive solutions when the light is excluded ; (b) in very rich 

 organic fluid even in the light. The organism can endure relatively 

 large quantities of free acid, and this quality was utilised in securing 

 cultures free from bacteria. In fluids the cell-division always occurs 

 in the mobile phase ; it takes place in the resting stage only when there 

 is a sufficiently firm substratum. 



Capacity of Adaptation of the Lower Organisms to Concentrated 

 Solutions.* — From experiments made on Euglena viridis, Chilomonas 

 pnramsecium, Malloimonas ploslii, Colpidium colpoda, and Paramecium 

 caudatum, Prof. A. Yasuda finds the power of resistance of Infusoria to 

 concentrated solutions to be much less than that of the lower algre and 

 mould-fungi. In the case of Euglena, the optimum concentration was 

 found to be, — for milk-sugar 17, for cane-sugar 15, for grape-sugar 11, 

 for glycerin 6, for magnesium sulphate 6, for potassium nitrate 2*4, 

 for sodium chloride 1 ■ 8 per cent. Somewhat different results were 

 obtained with other organisms; but, in general, the optimum conceutra- 

 tion was in proportion to the isotonic concentration of the medium. 



Zygospore of Polyphagus euglense.f — Mr. H. Wager has followed 

 out the formation of the spores and zygospores of Polyphagus euglense. 

 In the latter a rhizoid is put from the passive to the active cell, which 

 is larger than the former, and has a larger nucleus. The apex of the 

 rhizoid swells up and becomes the zygospore, into which the small 

 nucleus passes with its surrounding protoplasm. The large nucleus 

 of the active cell then approaches the smaller one, passing through an 

 opening in the cell-wall, but without fusion. The two again separate, 

 and the small nucleus increases in size till it has attained the size of 

 the larger one. Finally they unite after lying side by side for a time. 



* Arb. a. d. Bot. Inst. k. Univ. Tokio. Sec Bot. Centralbl., lxxx. (1899) p. 169. 

 t Rep. 68th Meeting Brit. Ass., 1898 (1899) p. 1064. 



