MORPHOLOGY. 61 



d. This growth takes place in the more highly orga- 

 nized plants directly in two portions, evidently apart 

 from each other, in the continual changes of whose va- 

 rious relationships is seen the entire aerial life of a plant. 



e. These different portions are the axis or stem, and 

 the leaf. 



f. The stem is the remaining original part of all 

 the aerial formations, is opposed to the leaf as being 

 its support, and constitutes the central system or axis ; 

 the leaf on the other hand appears as a peripheral divi- 

 ded portion, which may be looked upon as separated 

 here and there from the stem, and may probably be re- 

 garded as a secondary and again divided axis, but 

 which in its internal formation must be looked upon as 

 unsymmetrical. 



g. The axis increases both in length and breadth, 

 and divides by degrees like the under growth ; but 

 there is a very great difference between the growth of 

 the stem and that of the root, for the first developes 

 itself in length at certain periods, whilst the root is less 

 subject to such periodicity, and therefore increases at 

 all times. 



h. The leaf developes itself as it unfolds, and is not 

 only an extension and growth in length, but also one in 

 breadth, and this development equalty deviates from the 

 perpendicular direction of the axis. 



*. In the upward growth appear three evident 

 points, in the evolution of which its whole formative 

 power and activity is represented : these are, nodus, 

 leaf, and internodium. 



j. When we look at the place of origin of a leaf, 

 we observe a thickening of the axis, and a sort of in- 

 tangling of the vessels into a knot or nodus, imme- 

 diately beneath it ; above a nodus the vessels again 

 assume a regular and symmetrical course until they ar- 

 rive at the situation of another nodus, and thus along 

 the axis several internodii are seen one above the other : 

 according to the disposition of the internodial axes with 



G 



