Rothrock.] vOJi [Feb. 2. 



developed than in tlie Tupelo (Nyssa uiultiflora), or in a specimen of good 

 White Oak. However, in making comparisons of this kind, we must be 

 careful to make them at points equidistant from the centre ; and to note 

 whether these rays extend to the centre, or only part way in from the bark 

 toward the heart of the tree, as this latter circumstance determines their 

 age, and also generally their relative strength. In such species of timber as 

 have rays extending vertically over two or more inches, as in some 

 of the Oaks, the ray often indicates the line of easiest splitting, as is often 

 seen by the eflect of drying upon the exposed end of such timber. This is 

 not an invalidation of the statement that one function of the rays appears 

 to be to give lateral tenacity, i. e. to such portions of solid wood as lie be- 

 tween the rays. They form as it were a chain binding the periphery to the 

 centre, but offer no resistance to the separation of one woody wedge which 

 they outline, from another such wedge which is placed alongside. If this 

 be so, then such specimens of wood as have the rays ruptured by encroach- 

 ment of ducts or by any process of disintegration would be correspondingly 

 weakened. It is furthermore worthy of note that in such specimens of good 

 White Oak (Quercus alba), and good Pig-Nut Hickory (C. porcina) as upon 

 actual trial had proven to be the best, these rays were as a rule either most 

 numerous, or best developed, or both. 



Examined microscopically, the cells making up these rays present an 

 appearance Avhen viewed from the'side like figure D. That is to saj^ they 

 are quadrangular, thick walled and with numerous thin places in which the 

 primary cell wall may or may not remain. Their very appearance suggests 

 a somewhat easy communication between those (cells) which are adjacent, 

 and thus afford a probable explanation of the fact, that when the starch 

 made in summer by the younger portion of the tree is being conveyed into 

 the interior of the branches for winter storage, these rays appear to furnish 

 the most available avenues for accomplishing the work, and micro-chemi- 

 cal tests show that it is most abundant in them. While these thin or open 

 places in the cells of the medullar ray usually communicate with each 

 other, it is remarkable that they are much fewer in the sides toward the ducts 

 and fibres. 



It would be exceedingly interesting to know how far the focts indicated 

 by this paper would conform to the value of timber as determined by spe- 

 cific gravity. 



EXPLANATION OF ILLUSTRATIONS. 



1. Cross Section of Abies subalpiua wood fibre X 243. 



2. " " Tilia Americana " "X 242. 



3. " " Juglans cinerea, " " X 242. 



4. " " Carya porcina, " " X 242. 



5. " " Quercus alba " " X 242. 

 C. A and B. Flattened cells made in autumn. 



7. " " Larger cells which indicate growth of following spring. 



8. " " Open ducts seen in cross section. 



9. " " Medullary rays. 



