OF LOWER GIIEK.NS.VND PLANTS. 59 



and to systematise our knowledge. He lays great stress on the 

 pitting of the medullary ray-cells, a truly important character 

 which most of his predecessors had overlooked. 



His system of classification (abridged) is as follows: 



( Dadoxt/lon, Endl., ex p. = 



A. Hol'tiipfel klein. atternierend, oben I [Armicarioxylon, Kraus, 

 und unlen ahgepliittet, wenn mehr- J Conlawxi/lon, Felix, 



* 



reihig, alls-cits (polygonal abge- 

 plattet). 



Cordaio.vylon, Grand' Eury, 

 Amucariies, Goeppert, 

 Cordalics, div. auct.]. 



B. Hoftiipfel rundlich, grosser, nicht \ In this, with further detailed 

 gedrangt ; wenn mehrreihig, meist I diagnostic characters, he in- 

 gleichhochsteisd. J eludes the following genera : 



Taxoxylon, linger, ex p. 

 Piceoxylon, Gothan, 

 Piimxylon, Gothan, 

 Cedroxylon , Kraus, 

 Cupressinoxylon, Goepp., 

 Glyptostroboxylon , Con w ., 

 Taxodoxylon, Gothan, 

 Podocarpoxylovt. Gothan , 

 Phyllocladoxylo tt, Gothan. 



To these his later works (1908, 1910 A) have added more 

 genera, some of them well founded (such as Protopiceoxylon), 

 others which do not seem likely to stand the test of time, and 

 appear to be based on characters which are less good specific 

 criteria than he thought at the time the genera were founded. 



Jeffrey and his pupils have proposed many generic names, 

 frequently without either diagnosis or description, and nearly 

 always based on an interpretation of facts or theories which it is 

 difficult to follow. No adequate criticism of these genera can be 

 made here, but reference will be made to them from lime to 

 time in connection with the fossils at present under description. 



In 1907 Penhallow published his exhaustive book on the 

 North American gymnosperms, in which he describes and 

 illustrates many features of the wood whicji had often either 

 been forgotten or overlooked. He has a specially good section 

 on the medullary rays, and points out their great interest and 

 significance. Kegarding the rays he says (p. 101) : " No other 

 portion of the stem possesses so many elements of importance as 



