LECT. VII.] ANATOMY OF STEMS. 331 



Placing a very thin transverse section of the 

 stem of Horse Chesnut under the microscope, the 

 wood no longer appears solid and compact ; but of 

 an irregular reticulated texture -f-. In this state, 

 however, the concentric and divergent layers are 

 readily distinguished; the open spaces in the 

 former being evidently the transverse orifices of 

 divided longitudinal or vertical cells and vessels, 

 whilst those in the latter are the lateral openings 

 of horizontal cells ^. Let us now examine se- 

 parately the minute structure of each of these 

 parts as they appear in the stem of one year's 

 growth. 



1. The Concentric layers consist apparently of 

 longitudinal fibres, which are, however, appa- 

 rently not solid, but narrow tubes or oblong cells, 

 the sides of which are thick and nearly opaque, 

 and of vessels of different kinds. These are ar- 

 ranged parallel to each other, except where they 

 are separated by the divergent layers, as may be 

 seen in a thin tangental section 

 of any stem placed under the 

 microscope ; and is rudely dis- 

 played in the marginal plan, 

 in which a. a. a. a. a. represents 



t Vide Plate 6. Fig. 2. * represents the first state of the soft 

 wood or alburnum,/, the more perfect wood, and h. the orifices 

 of the large vessels of the wood. 



J Vide Plate 6, fig. 2.g. 



