1 66 ANATOMY OF THE GYMNOSPERMS 



particularly among those which are eventually silicified, and in 

 the present instance they serve to explain the mechanical weak- 

 ness of the tissue, the cellulose substance of which has undergone 

 a gradual molecular alteration consequent upon the action of an 

 alkaline solution - - possibly of a hot spring - - which has been 

 continued indefinitely. 



The Douglas fir is regarded as one of the most durable of 

 woods, and it is not surprising to find instances of its perfect 

 preservation under very adverse circumstances. Specimens of 

 Pseudotsuga macrocarpa, from the same beds as the Californian 

 juniper already described, exhibit the same absence of special 

 silicification, but they differ in a much more marked development 

 of fungus mycelia, and in a somewhat extreme alteration through 

 the action of free alkali, which has been carried so far that in the 

 summer wood the cell cavities are largely obliterated, while 

 the thinner-walled tissue of the spring wood shows definite col- 

 lapse. Apart from this there is no evidence of the removal of 

 parts through the action of decay, and we may conclude that 

 the fungus present had not produced any specific effect. Yet 

 another illustration is afforded by Pseudotsuga Douglasii from 

 Mystic Lake at Bozeman, Montana, where it was found under 

 eight feet of the old lake-bed deposit, which antedates a well- 

 defined and superimposed glacial deposit. The age of this for- 

 mation is open to discussion, as it may represent local glaciation 

 of recent date, while there is also a possibility that it may be 

 synchronous with the continental interglacial period, since the 

 absence of the tree from the same locality at the present day 

 leads us to suppose that its removal occurred in the time of 

 general glaciation, as may be inferred from other evidence (46). 

 In its external aspects the wood presents a remarkably perfect 

 state of preservation, exhibiting all the features of grain and 

 other structural details, even to an exhibition of the bordered 

 pits, which may be readily determined with a hand lens of mod- 

 erate power. Furthermore it was wholly free from infiltrated 

 mineral matter and was readily softened in boiling water so that 

 sections could be cut with the greatest ease. Internally the 



