﻿3 1 o BOTANICAL GAZE TTE [may 



matic membrane must be immediately formed on a freshly exposed surface 

 as it comes into contact, not with plasma, but with other media and espe- 

 cially water. Nevertheless, the determining causes cannot at present be 

 precisely defined, and it is hardly probable that the plasmatic membrane is 

 simply the expression of the physical surface tension, which is necessarily 

 always present. The latter may be of decisive importance, however, in the 

 formation by means of the molecular forces exerted by it, while at the same 

 time contact with the medium may cause the substances in the peripheral 

 film to be precipitated in an insoluble form, which redissolves when returned 

 to the interior of the plasma. Since a membrane is formed on every isolated 

 fragment of plasma, even when its vital activity is reduced to its lowest ebb, 

 it seems as if the actual exposure of a peripheral film induces the formation 

 of the plasmatic membrane. 



It is not my purpose to enter into a theoretical discussion as 

 to the minute changes which take place during the formation of 

 the plasmatic membranes, but merely to point out the fact that 

 v^henever the cytoplasm is exposed to a watery surface a mem- 

 brane is formed and that all membranes thus formed are structur- 

 ally identical, so far as can be revealed by the microscope. A 

 third internal plasmatic membrane which has never been con- 

 sidered in this connection is the nuclear membrane. It too 

 comes in contact with a watery fluid, the nuclear sap or karyo- 

 lymph. As we shall see from the following observations, it is 

 formed in identically the same manner as the tonoplast. It is 

 nothing more than a modified film of cytoplasm, and on account 

 of its similarity in structure and method of formation to that of 

 the ectoplast and tonoplast the writer regards it as one of the 

 series of plasmatic membranes of the cell. 



J 



THE FORMATION OF THE NUCLEAR MEMBRANE. 



In the history of every nucleus of the higher plants which 

 divides mitotically there are two stages in which this organ i 



consists of nothing but chromatin. The first of these stages 

 may be seen in any mother nucleus in its preparation for mito- 

 sis during the period of spindle formation. At this time the ^ 

 nuclear wall breaks down, the nucleoli and linin disappear, the \ 

 karyolymph becomes diffused throughout the cytoplasm, and by 

 the time the spindle is formed the only nuclear element that 

 remains is the chromatin which has assumed the form of definite 



