CONIFERAE. 8 1 



cannot be thus separated. In this way he arrived at the formation of the 

 groups of woods known as Pinites, Araucarites, Cupressinoxylon, and Taxites, 

 the first of which takes in most of the recent Abietineae, the second the 

 Araucarias and Dammaras and with them the Cordaiteae, as was said 

 above, the third the Cupressineae and Podocarpeae, the fourth the Taxineae. 

 To these were added the generic types Physematopitys answering to the 

 wood of Ginkgo, Protopitys which doubtless represents one of the woods 

 of uncertain affinity now named Arthropitys, which will be noticed again 

 presently, and the altogether doubtful Spiropitys. Unfortunately Goppert 

 has converted the groups of woods thus obtained into genera, and founded 

 numerous species within them on characters which are in some cases very 

 doubtful. His main results have since been gathered up by Kraus l and 

 extended by splitting Pinites into Pityoxylon and Cedroxylon, the first of 

 which takes in the firs, the second the rest of the Abietineae. Kraus has 

 also carefully examined the characters employed in the definition of species, 

 and has shown that the relative marks generally made use of up to that 

 time, breadth of the annual ring, width of the cell-lumina, thickness of the 

 cell-walls, number of rows of pits on the radial walls of the tracheides, 

 height of the medullary rays and their frequency, can either not be employed 

 at all or only with the extremest caution, because, as von Mohl 2 has shown in 

 his well-known treatise, they are liable to important modifications in the 

 different organs of the same tree, in stem or branch or root, and because 

 great individual fluctuations occur in different trees of the same species. 

 Essner 3 has supplied ample proof of the truth of these remarks as respects 

 number and height of the medullary rays, and Kraus 4 himself showed, by 

 application of diagnoses in Goppert' s manner, in the case of the connected 

 stem and branch of a piece of wood from the lignite of the Rhon, that 

 if the two had been found separate they would have supplied two 

 good species. The characters of Kraus' generic groups are as follows : i. 

 Araucaroxylon (Dadoxylon, Endl.). Radial pits of the tracheides either 

 in one row with contact and mutual compression, or alternating in several 

 rows and becoming polygonal from mutual contact. Medullary rays in a 

 single row on the tangential section. 2. Pissodendron. Distinguished from 

 ArauCaroxylon only . by the presence of several rows of medullary rays. 

 Witham 5 calls such forms Pitus, Brongniart Palaeoxylon. 3. Cupres- 

 soxylon. Radial pits of the tracheides in a single row, circular, not 

 touching one another, or in several rows very commonly in the root ex- 

 ceptionally in the stem, not alternating and polygonal but round and in 

 irregular transverse rows. Resiniferous parenchymatous wood-cells in 



1 Kraus (1) and (3), and Schimper (1), p. 363. '' H. von Mohl, Einige anatomisch-physiologische 

 Bemerkungen iiber das Holz der Baumwurzeln (Bot. Ztg. (1862), p. 225). 3 Essner (1). * Kraus 

 (1), p. 185. '> Witham (1). 6 Brongniart (2). 



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