184 BAILEY AND TUPPER. 



secured by the WTiters, Figs. 1, 3, and 4- It seems probable, however, 

 from the study of available data, that, although in most cases the 

 length of the tracheids does not become constant in the older wood of 

 individual stems of coniferous plants, the normal length-on-age cur^■e 

 for any particular species is of the general form illustrated in Graph 16, 

 Fig. 5. 



In any given plant, the length-on-age curA'e, or one or more portions 

 of it, may deviate from the norm of the species, owing, in all proba- 

 bility, to the effects of various environmental factors. Thus, stunted 

 or depauperate plants appear to have depressed curves, Graphs 12, 

 12a, oa, 5b, 14, 14ft, and 8. Furthermore, the distorted tracheary 

 tissue, formed subsequent to injury or in response to abnormal growth 

 conditions, frequently possesses shorter tracheids than normal tissue, 

 A, Graphs 13 and da. Similarly, tissue formed in regions of the plant 

 where there are considerable mechanical stresses, e. g. at the junction 

 of stems and roots or stems and branches or in bent or twisted stems, 

 tends to have shorter tracheids than normal straight grained tissue. 

 This is shown very clearl}' in the following taljle: 



TABLE IV. 



Pinus Strobus. 

 Stems one year old. 



Length tracheids mm. 



Specimen No. 1. 

 Wood from vicinity of branch wliorl 0.43 



Wood from stem between branch whorls 0.82 



Specimen No. 2. 

 Wood from vicinity of branch whorl 0.62 



Wood from stem between branch whorls 0.96 



Specimen No. 3. 

 Wood from vicinity of branch whorl 0.65 



Wood from stem between branch whorls O.Sl 



Specimen No. 4. 

 Wood from vicinity of branch whorl 0.65 



Wood from stem between brancli whorls 0.99 



Si)ecimen No. 5. 

 Wood from vicinity of branch wIkuI 0.71 



Wood from stem between branch whorls 1.16 



