30 Objects for the Microscope. 



seeds have two lobes, or cotyledons ; the flowers are 

 arranged in four or five. The wood grows by the addition 

 of cells, in circles, to the exterior of that last formed, and 

 we see distinctly the open cells of the pith in the centre ; 

 the medullary rays running from the centre to the bark at 

 intervals, with sap-vessels and cellular tissue in circles, as 

 they were added on. 



CEDAR OF LEBANON, 



a firm, dense wood ; the cells are very minute, the circles 

 very distinct ; each circle is a year's growth, and the medul- 

 lary rays are very fine and numerous, radiating from the 

 centre. Those dark bands forming the circles are made up 

 of vascular tissue, or woody fibre, composed of long pointed 

 cells, which overlap one another, and deposit internally a 

 strengthening wall of a substance called scleragen, which is 

 most abundant where not only density but great power of 

 resistance is required. When young these woody fibres 

 conduct the sap with facility through both stem and 

 branches, especially of the fir tribe ; but after they are 

 thickened they only afford support, and become what car- 

 penters call " heart-wood." The sap-vessels of trees are 

 those nearest to the bark, which makes the barking of trees 

 so dangerous to their life. 



SECTION OF PINE. 



Look next at this section, because it shows some pecu- 

 liar dots on that same woody fibre, called glandular dots, 

 and which are remarkable as belonging to that tribe, and 

 also at one of the yew tree (Taxus). 



SECTION OF YEW. 



Iii this section, if vertical, there is a beautiful com- 

 bination of spinal fibre with coniferous pits. 



These pitted structures require explanation, especially as 

 those of the pine or common deal are used as tests of the 

 defining power of the object-glass. The pits in coniferous 

 wood are surrounded by a broad rim. 



The origin of the pitted cell is in the unequal deposit of 



