Nos. 451-452.] AA'ATOAfV OF THE CONIFERALES. 



The recognition of the resin cells presents no difficulty in the 

 great majority of cases because of the abundance and depth of 

 color of the resinous contents. This finds its most complete 

 expression in Taxodium, Sequoia, Cupressus, etc. In Abies, on 

 the other hand, where these cells have experienced extreme 

 numerical reduction and where there also seems to be a corre- 

 sponding reduction in their secretory power, it is impossible to 

 recognize them in this way. In such cases it is otten possible 

 to distinguish them by their slightly different form and some- 

 what thinner walls as compared with the adjacent wood tracheids ; 

 by their situation slightly in advance of the outermost row of 

 summer wood tracheids ; and most particularly by their pitted 

 terminal walls when the latter lie near the plane of section. 

 This last feature may also be relied upon in all other cases when 

 any element of doubt is involved (Fig. 36). In longitudinal 

 section the characteristic form of the cell serves to distinguish 



The resin cells sometimes occur in pairs, but more <;enerally 

 as isolated structures separated by one or more tracheids. Ihe 

 terminal walls are transverse and more or less strongly marked 

 with simple pits. The side walls, especially the radial, are pro- 



