138 



X. THE CONIFEROUS STEM. 



same time spiral bands and bordered pits, serve as a transition to 

 the typical trache'ides having bordered pits only. 



As to the directions of the sections which we shall need, as 

 well as the distribution of the tissues which we shall study, 

 we can first of all get a general idea by means of the lens, or 

 the low power of our microscope used as a lens, using for the 

 purpose a piece of fresh stem not more than half an inch in thick- 

 ness. The distinction 

 of wood and bast, the 

 annual rings, resin 

 passages and medul- 

 lary rays will then 

 be distinguishable (see 

 Fig. 50). 



In our careful study 

 we will use a high 

 power, and as we shall 

 also take cognisance 

 of the contents of the 

 elements, and especi- 

 ally concern ourselves 

 with the cambium, we 

 think it preferable to 

 use material which 

 has been preserved in 



FIG. 50. Piece of a four-year-old stem of the Scotch alcohol. Fresh wood 

 Fir (Finns sylvestris) cut in winter, q, appearance in 



cross-section; I, in radial longitudinal section; t, in tears at the cambium, 



tangential longitudinal section ; f, spring wood ; s, -i -i n -i 



autumn or late summer wood ; m, pith ; p, primary and dl 7 wood does not 



wood ; 1, 2, 3, and 4, the four successive years rings of differentiate SO well. 



the wood ; i, i, limits of the annual growths ; MS, med- .,111 



ullary rays as seen in cross-sections in the wood ; ms', Alcohol has the further 



in longitudinal section; ms", as seen inside the bast ; ^rmhlp ^vflntacrp thot 



ms"', as seen in tangential longitudinal sections; c, double advantage, tnat 



cambium ring ; b, bast zone ; h, h, resin passages ; br, it will have dissolved 

 the primitive bark ( x 6). 



the abundant resin out 



of the wood, and will have fixed the cell-contents. It is desir- 

 able that the pieces of stem which are to be preserved in alcohol 

 shall be moderately thick, since the size of the elements con- 

 stituting the wood of a Conifer is progressively greater up to a 

 certain age. In order to fix the cambium in an active condition 

 the material is best collected in June or early in July, i.e., at 

 the time when the cambium is most active. The material must 

 include the periphery of the stem, but on the other hand need 



Ir 



ms' 



