272 HISTOLOGY OF STEM OF THE WAX PLANT 



twenty or thirty years ago, showed that the "histological elements of 

 the wood are not in open communication with each other and that the 

 bordered pits of the wood cells (and the vessels of foliage trees) are 

 not actually perforated, but closed by fine membranes." This is 

 confirmed by Sachs, in the experiment he gives on the same page, 

 namely, by filtering through the wood of a conifer a fine emul- 

 sion of cinnabar, the cinnabar not penetrating the wood cells. He 

 states that this is also true of foliage trees. In some thin sections of 

 wood I thought I could see the connection between the cells, but 

 could never satisfy myself that there really was one, as it is very 

 difficult, and in fact a matter of chance, to get a section showing clearly 

 the edge of the wall of a duct. 



The ducts are surrounded by small wood cells and are generally 

 in groups, sometimes two being contiguous and presenting the appear- 

 ance of one large one having a longitudinal partition. At the point 

 where the ends of two ducts meet, the walls are not pitted around a 

 circle indicating the point of union, but in the central portion of the 

 transverse wall is a circular plate that can be removed, as some sec- 

 tions show a space that was formerly occupied by the disk, and in a 

 slide of macerated wood cells we find these round perforated portions 

 of the ducts abundant. On pi. II, fig. 3, is figured the end of a duct, 

 showing the circular space mentioned, and fig. 3a of the same plate 

 shows the disk that formerly occupied it. 



The ducts are formed in the cambium, and while increasing in 

 thickness, their walls become pitted. These pits are present in both 

 the tangential and radial faces and also where the ducts meet end to 

 end. Some portions of the walls, however, are without pits, but their 

 relation to the position of the cell I have not determined, as I have 

 only noticed the fact with certainty in longitudinal sections, and, of 

 course, it is not possible to say what occupied the place before it had 

 been cut off. 



Wood Cells 



These are very irregular in shape, and some of the forms they 

 assume are shown on pi. II, figs. 5-5C Their diameter is quite 

 constant, being about 15 p. Their length varies, as a glance at the 

 plate mentioned above will show ; some are 5 mm. in length and others 

 but .15 mm. They may easily be obtained for examination by macer- 

 ating a portion of the wood, or by boiling a piece in Schultze's solution. 



