﻿3oS BOTANICAL GAZETTE [may 



In all of these particulars the structure of the mature nucleus ■ 

 bears a very striking resemblance to the vacuole. It is a cavity 

 containing a watery fluid — -the nuclear sap or karyolymph — in 

 which lie imbedded the chromatin thread and nucleoli. Struc- 

 turally the nuclear sap may be compared to the cell sap of the 

 vacuole; the chromatin and nucleoli maybe compared to the 

 solid bodies of reserve food materials found in the cell sap; 

 and finally the nuclear membrane may be compared to the 

 tonoplast. These two latter structures not only bear a general 

 resemblance to each other, but, as we shall demonstrate later, 

 their origin and method of formation are identical. 



This resemblance of the nucleus to the vacuole is particularly 

 evident in the cells of sporogenous tissue, where the vacuole is 

 not usually present and where the nuclear cavity occupies the 

 greater part of the cell. In many cases the nucleus was repre- 

 sented as constituting fully two-thirds of the cell contents {^fig- 

 ij), and the cytoplasm in such cases was a mere zone between 

 the nuclear membrane and the cell wall. As we know so little 

 in regard to the direct function of the nucleus in relation to 

 metabolism, we are unable to account for the large size of the 

 nuclear cavity in these sporogenous cells. But as these cells 

 are characterized by the absence of a vacuole, this fact suggests 

 that the nuclear cavity may here function as the vacuole func- 

 tions in the vegetative cells. The writer regards this suggestion 

 worthy of consideration, since the function of the nucleus is 

 coming to be regarded more and more as an essential factor in 

 constructive metabolism. 



THE PRESENCE AND FORMATION OF PLASMATIC MEMBRANES IN 



THE CELL. 



Of late years much attention has been given to the impor- 

 tance of plasmatic membranes and their relationship to osmosis. 

 As a result of the investigations of Nageli, Traube, and more 

 particularly of Pfeffer, the cell is now regarded as an osmotic 

 system composed of a series of membranes. In the typical 

 plant cell there are three of these membranes commonly recog- 

 nized, namely, the cell wall, the ectoplast, and the tonoplast. 







