156 VEGETABLE CELLS. 



of organic matters from the contents ; one passes into the 

 other without any definite boundary. 



In reference to the formation of membrane, therefore, 

 we may establish the following distinctions : In CELL- 

 FORMATION, an universal and momentary production of 

 new membrane takes place. In APICAL GROWTH, an uni- 

 lateral and continuous formation of new membrane appears. 

 In UNIVERSAL GROWTH, wJdcli follows both cell-formation 

 and apical growth, an expansion and thickening of the 

 newly-formed membrane takes place. 



The apical growth may begin in a cell in two ways, in 

 reference to its relations to the life of the cell in time 

 and space. In the first case, the apical growth begins 

 at once with the formation of the cell. A portion of the 

 contents becomes individualized, and secretes membrane 

 over its whole surface, whereby the cell is formed ; this 

 new formation of membrane continues at one point of the 

 surface, and the cell goes on growing in this direction. 

 The apical growth is here immediately connected with 

 the cell-formation. It begins directly after the origin of 

 the cell, before the universal growth has commenced. 



In the second case, on the contrary, the cell first ex- 

 pands by universal growth. The membrane becomes 

 thickened; the contents are applied upon the internal 

 surface. Then a portion of homogeneous mucilage is formed 

 at one point of the surface, beneath the membrane, and 

 with this begins a new apical growth, as I have above de- 

 scribed it. The apical growth, therefore, does not here 

 follow immediately the cell-formation, but the universal 

 growth of the cell. It may occur, either in a cell with- 

 out apical growth, or in a cell with this, as on the lateral 

 part of a cell-branch growing at the apex, and always 

 appears as a growing-out of a point of the surface. 



Through the first hind of apical growth the nascent 

 cell grows longitudinally. By the second kind the cell 

 branches. 



The apical growth is also variable in its duration. It 



