96 



LECTURE VII. 



two interfoliar parts. These leaves and nodes now continuaUy undergo repeated 

 divisions during their growth, which follow a quite definite and exactly known law, 

 both as regards their direction in space and also their sequence one upon the other 



in time. 



It is not necessary here to enter more particularly into these matters. 



We shaU be able to apprehend in the main the relation between growth and the 



repeated division of the cells into two, if we observe that in our figure the parts 



Fig. 9S.— Longitudinal section through the apex of Chara. Each portion of tissue bounded by a thick 

 contour has originated from a segment, i. e. from a cell immediately segmented off from the apical cell. 

 (Partly diagrammatic.} 



distinguished by t, b, respectively, always proceed from a segment of the apical 

 cell ; and that with the increasing growth of the same the number of division walls 

 contained in them increase also. If we compare, for example, the portion f h" 

 included by the thick contours, with the younger portion f b\ we easily perceive 

 how with the growth of the former, which previously possessed exactly the form and 

 size of the latter, the cell-divisions have proceeded; and if, further, we take into 

 consideration the portion i" b'" , in like manner enclosed by thick contours, we again 

 recognise how, with progressive growth, the cell-divisions have proceeded in definite 

 order also. 



The development of the stomata in the epidermis of a leaf (Fig. 96) may serve as 



