Study of Spirogyra nitida. 257 



changes are very gradual and show plainly the structure of 

 the nucleus and its contents. 



This weak solution of palladions chloride was run grad- 

 ually under the cover glass, its action on the cell being 

 carefully watched. The first visible result was a sharp 

 rounding off of the nucleus from the cell, though the nuclear 

 threads were not broken. By this rounding off the nuclear 

 membrane became plainly visible, and appeared to be a 

 clear, homogeneous, doubly refractive bounding layer. 

 Even by aid of an oil-immersion lens it was impossible to 

 detect any structure in it. The nuclear substance mean- 

 while assumed a brownish appearance, which was probably 

 due to a deposit of metallic palladium, and its granular 

 structure became very marked. In many nuclei there 

 appeared to be a mass of tangled threads in the meshes of 

 which lay the more fluid substance. The threads suspend- 

 ing the nucleus could be distinctly traced through the 

 nuclear membrane and into the granular mass of the 

 nucleus. 



The nucleolus showed a dark bounding layer of double 

 contour. Its substance remained homogeneous, but became 

 much more refractive than is usual. The dark layer is 

 undoubtedlv a true membrane dividing the nucleolus from 

 the nucleus, as stated first by Macfarlane,* and confirmed by 

 subsequent investigators. It was distinctly visible and in- 

 variably present. 



These changes took place in from 8 to 10 minutes. A 

 continuation of the action of the very dilute palladions 

 chloride caused the suspending nuclear threads to rupture, 

 and in so doing generally displaced the nucleus. Where 

 this happened the nucleus was observed to be incased in 

 a protoplasmic pellicle which was distended until it was 

 much larger than the body which it enclosed. The sus- 

 pending threads were seen to penetrate this pellicle. 



A further treatment of the cell with this reagent caused, at 

 the expiration of half an hour, a complete balling together 



* Trans. Bot. Soc. Edin. Vol. 14. 



