OF LOWER GREENSAND PLANTS. 



B. Secondary tracheids without spirals or with 

 very fine and delicate markings. " Abie- 

 tinean pitting " in ray-cell end-walls notice- 

 able. 



1. Resin-canals both vertical and horizontal 



present in wood and in multiseriate 

 medullary rays. 



2. Resin-canals only vertical in the wood. 



Medullary rays all uniseriate normally. 

 c5. Resin-canals normally absent. Resin-con- 

 taining xylem - parenchyma generally 



Cedro>rt/!on. 



absent or present in exceedingly small 

 quantities. 



C. Typical " abietinean pitting " generally 

 absent. Resin-canals absent, but resin- 

 parenchyma plentiful. 



a. Medullary ray-pits small, roundish, l-oo 1 Cupressinosylon. 



per tracheid-liekl, commonly 1-6. 



b. Medullary ray-pits large, chiefly 1, some- j 



times 2 per tracheid-field, tending to be ^ Podocarpoxylon. 

 laterally extended. 



It must be understood that all tho above are " pseudo-genera," 

 and are founded only for convenience of description. Individual 

 species, if well petrified, can often be identified and associated 

 very closely with living genera or species. I think it is 

 extremely important that no two specimens from different 

 countries and different horizons should be identified as the same 

 species, unless there is sufficient absolute proof that they are, in 

 all their parts, truly identical. I am in the fullest agreement 

 with Halle (1913), when he says (p. 369) " The fact of two 

 groups of forms being described under different names does not 

 imply, therefore, that they are necessarily distinct species, but 

 only that they cannot at present be proved to be identical." 

 In this way only can ultimate order bo attained, for, as Halle 

 points out, the piecing together of the various organs of a plant 

 then only results in the dropping of some of the names and is 

 very easily accomplished ; while if different forms have been 

 included in the same " species,'' and stratigraphical and phylo- 

 genetic conclusions drawn therefrom, the confusion is endless. 



