170 OONIFEBALES [CH. 



subject is interesting and beset with difficulties but well worthy 

 of more thorough treatment than it has so far received. Though 

 petrified Coniferous stems are usually represented by the secondary 

 wood only, the phloem and cortical tissues are sometimes preserved- 

 and afford useful information. Examples of petrified phloem and 

 other extra-xylem tissues are described by Lignier and other 

 authors. In his description of silicified plants from Franz Josef 

 Land, of Lower Cretaceous or Upper Jurassic age, Solms-Laubach^ 

 includes some pieces of Coniferous bark showing patches of peri- 

 derm alternating with secondary phloem consisting of sieve-tubes, 

 phloem-parenchyma, and fibres, also some stone-cells. Some of 

 the sieve-tubes are shown in fig. 718, B, with well-preserved sieve- 

 plates, a feature very rarely preserved. There is not enough wood 

 associated with the phloem and periderm to serve as a means of 

 identification, but Solms-Laubach speaks of the bordered pits on 

 the tracheids and the pits of the medullary rays as indicating 

 Pityoxylon or Cedroxylon. 



A new generic name Vectia has been instituted by Dr Marie 

 Stopes^ for a mass of petrified phloem which she compares more 

 especially with the phloem of recent Conifers : while recognising that 

 the specimen cannot be assigned with confidence to a particular 

 group of Gymnosperms I venture to think it is almost certainly 

 a portion of a Cycadean stem. 



Reference has already been made in the section devoted to 

 the anatomy of recent Conifers to the relative importance and con- 

 stancy of different characters from a taxonomic point of view and 

 this question need not be further considered. The method of 

 classifying coniferous wood in general use is based on a scheme 

 proposed by Kraus^. A modified form of this scheme was pub- 

 lished by Schenk* and more recently Penhallow^, Jeffrey, Lignier, 

 Gothan, Dr Stopes, and other authors have considerably extended 

 our knowledge. Dr Gothan*, whose memoir on the anatomy 

 of Conifers contains much valuable information, employs se^veral 

 generic names denoting identity with recent types, and while 

 admitting the great advance made by him and other workers in 



1 Solms-Laubaeh (04). = Stopes (15) p. 247. See p. 419, Vol. m. 



3 Kraus in Schimper (72) A. p. 363. 



" Schimper and Schenk (90) A. p. 860. 



° PenhaUow (07). « Gothan (05). 



