286 Remarks on the Structure of Wood. [Ma y , 



be drawn from them, will aid essentially in determining genera 

 and species. Here is at any rate an interesting field of research, 

 and though very important results may not grow out of it, yet the 

 carious and interesting sti'ucture, beautiful in all respects, will 

 itself repay the observer abundantly for all his pains and labors. 

 There is one point which renders the investigation^more interest- 

 ing, and which adds also to their value, 'the fact that the observa- 

 tions may be made with a common single lens of an inch, or an 

 inch and a half focus, so that no expensive apparatus is required 

 to conduct them to a satisfactory issue. To prepare the wood for 

 examination it is necessary only to make a clean transverse sec- 

 tion of the stem with a sharp knife, being careful not to bruise 

 the surface in the operation; or what is better in some cases, pro- 

 cure a thin shaving by a sharp plane in the same direction. This 

 on being placed between glass plates with gum arable, will give 

 a very satisfactory view of the structure of the wood. 



No doubt some botanists will regard the mode as rather coarse 

 and attended with too little nicety and expense, still it is one 

 which will be found to answer very well and to be within the 

 practical reach of all, whereas an expensive microscope, together 

 with an expensive slicing instrument places it beyond the means 

 of most persons who study botany in this country. 



As it is not my purpose at this time to enter upon a detailed 

 description of the structure of wood as it appears under a single 

 lens, I shall proceed at once to give a very brief description of 

 the four samples of wood, the structure of which is given upon 

 a steel plate. These were selected almost at random, and are less 

 beautiful and interesting than many others, as any one may satisty 

 himself by inspection and comparison. 



In the examination of wood the principal parts to be noticed 

 are the tubes or sap vessels, which may be divided into primary 

 and secondary, and the medullary rays both of the wood and bark. 

 There is but little diversity in the arrangement of the medullary 

 rays; in some woods those which commence at the pith extend to 

 the circumference while in others they never do — their thickness 

 too is quite different, yet in general arrangement it is the same in 

 all woods. The tubes or vessels however differ both in size and 

 arrangements in different species of vegetables. The primary, 

 which are the largest and most conspicuous, are first formed in 

 the spring of the year; tlie secondary are distributed through the 

 remaining part of the annual layer in a very peculiar manner, and 

 this arrangement in different genera at least is quite different. 



In illustration of the foregoing statements I now refer the read- 

 er to the engravings. PI. 3, Fig. 1, is a section of the chestnut, 

 enlarged about four times. It consists as will be seen of series of 

 segments of rings which are the annual growths of the tree; each 



